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AIRHEAD Electrical Hints and Problems

© Copyright 2014, R. Fleischer

I HIGHLY recommend you FIRST read article 14A.....which begins with basic
electricity... lots of HINTS on problem areas in that article!

It will be to your advantage to read this:
ONE of the reasons to read it is because I removed all that multimeter
information from the below article!  It contains a lot of information on
multimeters (often called VOM's) & test lights. 
REALLY worth your time to read...and absorb!
If you have always been confused by electrical things, you will have
a pretty good working understanding after reading my electrical articles. 
But, do the Basics reading first, so you understand electricity.  There
are a number of electrical articles on this website,,,,all in one section of
the Technical Articles List.

I do not expect you to understand (nor, hardly remember) everything that
is in the below article.  If you read this entire article, slowly, and think about
what you are reading, and remember some details, that is probably the best
I can hope for.

I recommend purchase of BOTH a test lamp and a very small in-expensive digital multi-
meter that will fit in the tool tray on the bike.
  A simple test lamp can be very helpful in
tracing down problems.   A multi-meter is NOT a necessity for an on-bike tool. If you
decide to not have one on the bike, then get a larger size one to have at home.  If you
purchase a test lamp get one with a steel pointy tip, NOT a battery type, & should be the
type that has a longish stranded insulated wire with a decent-sized alligator clip (if not at
least 4 feet long, lengthen it).  

***I also recommend that you SAVE your next headlamp bulb (car or motorcycle) that
has failed on either high or low beam (where the other beam is OK).    You can use that
as a high power lamp to trace short circuits, that are blowing fuses and for other testing....
see later in this article.  This is a powerful method!  The headlamp bulb draws a lot more
current...(but a SAFE amount)...than the tiny lamp in the 'test lamp with sharp tip'; and
thus is quite useful as both an indicator AND for use as a safety fuse that does not
burn-out, if testing for short circuits.
  Make up such a power-lamp to have a socket
with wires attached, although you could use soldered wires onto the lamp.

***A test lamp with sharp prod, a multimeter, and a power test lamp, will cover
99% of electrical problem analysis!!

I recommend you make up a VR jumper wire; use insulated stranded conductor wire;
attach 1 standard 1/4th inch male push-on connectors at each end.   Make this jumper
about 4 to 6 inches long. Put it in your ON-BIKE tool kit. Its purpose is to allow
bypassing of the Voltage Regulator; for testing, or, if the VR fails. 

Bi-yearly maintenance of your electrical system is a very good idea.   You should
disconnect electrical plugs, clean contacts.  Use a contact cleaner, perhaps after mild
abrasive techniques, perhaps use a clear silicone grease or spray Caig product to protect
against atmospheric effects like corrosion.   There are premium contact oxidation
prevention products on the market, the best that are easiest to find are probably made
by Caig Laboratories.   Caig's products are highly recommended by me; particularly
for sensitive areas, such as K bike computer pins; but they are excellent for any
electrical connection that might corrode from atmospheric effects. There is another
premium product available.  See my chemicals, etc., article:
Once the contacts are clean/shiny, use of common dielectric grease from the autoparts
store will protect against atmospheric effects for a very long time.  I sometimes use
the Caig's protectant AND the grease; or, Caig's final special coating products.   A full
electricals check does not take all that much time, and you will then find it convenient
to inspect the diode board factory solder points, alternator connections for overheating
& tightness, brush lengths, 1981+ models have heat sink paste/grease to change on the
ignition module (except last versions that use riveted assemblies), etc.  Pay particular
attention to the male prongs and mating female connections of the STARTER RELAY.
Three hours of time well spent, every other year.

***The BMW factory used a contacts/connections protective liquid before shipping
the bikes.  The substance used was CRC 5-56. I have no problem if you want to coat
connections AFTER cleaning them to shiny, with this product.

Measurements of voltage can be taken on your airhead with various items turned on
or off, such as the headlight.  Except for the heated grips circuits, voltage drops of over
1/4 volt in any wire or switch or across contacts will indicate that there is a problem.   
When measuring voltage drops, for most types of circuits, you will get a more accurate
reading by connecting the multi-meter + (positive) lead to the battery + terminal, & using
the multi-meter - (negative) lead as the test prod.    Doing it this way means that you
need not subtract voltages from each other; as you get a direct reading of voltage drop.

Be sure that your Airhead's SOLID brown wires...grounds, earth, chassis, battery -,
are secure, everyplace.   There are places that are known problem areas, such as the
front coil mount & grounding wire(s) on the R65 early models....due to cracked
mounts.   Many airheads have a master grounding area, located on the left side of
the frame, under the fuel tank.  Check the inside of the headlight shell too.


In some repair manuals, it is wrongly said, or wrongly implied, that you can use
a voltmeter connected in a series connection, to measure such as current drains.
This is absolutely NOT TRUE.  You use a ammeter, or milliamp-meter function,
for current flow.  


STOCK BOARDS. However, the information in this section covers lots more than that...
so read it fully! 

The large power diodes (which are pressed-in-place) used in the diode boards are Motorola 1N3659 (cathode to case) and 1N3659R (anode to case).   There may well be other manufacturer's numbers that will fit there; and you are LIKELY to NOT see these Motorola part numbers.   Three of each type of power diodes are used.  No matter whose make of diodes are used, the top row are the same part number, and the bottom row are the other part number; and the difference is that the diode polarities are reversed from each other.  They are all rated at 50 volts, and 30 amperes at 100° C.    Some alternator repair shops may stock similar diodes.  Generally any diode rated at 30 amperes or more, that will fit, will work just fine.  AGAIN!...MIND THE POLARITY...all 6 are NOT the same!    You may use higher rated diodes such as the 1N3660 and 1N3660R (100 volts) or 1N3661 and 1N3661R (200 volts); or, as mentioned, most alternator repair shops have diodes that will work OK.  Be careful pressing them in and out.
The solid wire from these diodes SHOULD BE FOLDED OVER and soldered along the length of that FOLD, onto the printed circuit board.  If need be, scraping away (or use paint remover) the coating over the copper on the board, to gain an adequate soldering area, before soldering.  This folding over and soldering was especially critical on the hotter-running RS/RT faired models, the original Werhle manufactured boards failed due to that problem (of not being folded over).   It is better to use a 50-50 solder, adding rosin flux, rather than 60-40 electronics solder. 50-50 melts at a considerably higher temperature and holds up better in THIS application. Plumbers wire solder is usually 50-50.  Be sure to use rosin flux (plumbers solder usually has no flux core).  If your large diodes on the diode board are showing signs of heat distress at the solder joint of that diode wire to the PC board then they need re-soldering (even if already folded).   IF the wire is NOT folded over, you CAN use 50-50 solder which has worked for me; but, the BEST fix is to drill a tiny hole through the copper printing material, and add a piece of wire, folding it over and soldering it to the PC, and also under the board, have it tightly wrapped and then soldered on the diode lead (clean well first or it will not solder correctly).   That job, for all 6 diodes, is QUITE a bit of a problem for many of you, trying to get the soldering iron underneath the printed circuit board.  I have gotten decent results by cleaning the soldering area pad and using 50-50 solder, on the 'bad' boards that come without folded-over leads.

If you are going to test the diode board a visual inspection, especially the solder joints, is the first thing to do.   Then
use an ohmmeter (or diode test meter function) that produces enough voltage/current to turn on the diodes in the forward direction, and thus check the forward diode function.  Reverse the leads and also check the reverse diode resistance.   The forward resistance or diode tester readout (which may be in voltage) is very low compared to the resistance in the reverse direction.   DO NOT have the battery of the motorcycle connected when testing the diode board in the bike.  All the diodes should be roughly the same.  Anal types can repeat the tests when the board is heated to approximately 200°F.  

The best diode test is with a transformer that supplies ~5 to ~15 volts AC, connected in series with a brake lamp or turn signal lamp (not a small lamp of lesser current drain), and the diode tested in this series circuit.  Full brightness is shorted diode, half brightness is proper, no lamp illumination at all is an open diode.   You can modify an old high intensity desk lamp that has a lamp and transformer, or make up something else.  The June 1999 issue of AIRMAIL has a long article on diode boards by OAK.   A separate article on diode boards and their grounding wires, etc. is on this website:

NOTE!    It is perfectly acceptable to use an application...or two or three....of any common gel type paint remover product...on the outer diode board printed enable removal of that pesky paint coating.  You do not have to re-apply paint later.    If using paint remover, use a water dampened cloth to remove the excess and then clean the board soldering area to shiny condition, before doing any soldering.  I use 50-50 plumber's solder, adding soldering rosin (soldering rosin is available in all hardware stores in a tiny can, it helps clean and prepare the joint as you solder), to make a stronger joint.  DO NOT use common electronics solder, which is typically 60-40.  Removing the coating will enable easy soldering of the diodes.  One of the indications of problems is when the solder joints at the 6 large diodes is discoloring and otherwise deteriorating upon a simple visual inspection ...the board need not even be removed to see is right in front of you with the aluminum cover removed.  FIX those joints!  Be sure the battery is disconnected!   Use an adequate sized soldering iron. Even a low power iron can work OK, if the iron tip is massive.

2.  ****CRITICAL ITEM****!!!
Unless you have an aftermarket EnDuralast Alternator...NEVER remove the outer timing chest cover without first disconnecting any and all leads at the battery negative terminal.  IF you have ONLY the large diameter black battery negative lead at the battery negative, then you CAN disconnect at the speedometer cable hollow bolt, and there is no need to unfasten that heavy wire at the battery negative.   If you have other wires at the battery negative post (at the battery itself), you should disconnect all of them at the battery negative, so as to be SURE there is no grounding going on, such as through a power jack, etc.  Failure to heed this hint can result in ruining a diode board during removal of the outer timing chest cover.   The accessory jack may be grounded in its mounting, and may not be, depends on model you use. Anything that provides an alternative grounding for the battery is suspect.   Safest ground for 'such things' is back to the frame, not the battery negative; so keep that in mind when installing accessories.   NOTE that the original plastic cover for the BMW accessory jack was 1 piece rubber or plastic and eventually broke from flexing.  You can replace it with the pricier, but far better one from a K model, and the part is:  61-12-2-303-574.  There are other jacks, of course, that work fine.  Just be aware of the possibility of a JACK grounding problem.

At the hollow speedometer cable bolt, disconnecting is made easier by clipping, filing, or cutting the lug, so it JUST fits OVER the screw, so the screw does not need removal, only loosening.  Be sure the washers are there.  That hollow bolt is modestly fragile, don't over-tighten, and be sure it has the the two flat washers..  If one is a waverly washer or lock washer, that will ensure there is no need to excessively tighten.  Just barely snug with a 10 mm short wrench is all the tightness that is needed here.

3.   Starter circuitry, basics:   the /5 bikes, and ONLY the /5 bikes, have a different type of starter relay (and an additional function) from all of the rest of the later Airheads.  In the Slash 5, once the engine starts, the rising alternator output is used to prevent the starter relay from being accidentally operated.   The original stock  /5 relay had a problem, that could cause one to think the battery was bad or failing.   The /5 relay has a very simple transistor circuit inside.  It has a faulty design.  In cold weather, and/or sometimes with just a slightly weak battery, the transistor fails to operate correctly (its 'gain' is greatly reduced), and the relay will vibrate slowly rather than stay pulled-in, when the starter button is actuated.  This results in a noise called 'the cricket'.  "Oak" Okleshen coined that name, Cricket, in the early 70's.  ... and of course the fix is called 'The Cricket Fix'.   The sound of the Cricket is sort of a clackety-clackety at a fairly fast rate.  Both that starter relay....and usually the large solenoid relay on the starter motor,... are doing the clackety dance together.   The result is no starter  cranking function, just the noise, and is very similar to what one might expect with a near dead or very low charge in a battery in a car.  The proper fix is to remove the  /5 relay (located in a metal can, left side of frame backbone under the fuel tank, and is the furthest forward item), open it up, and make a few simple changes.    There is a complete illustrated article on a permanent fix for the relay on this website at:  which is article 37.   I still see them once in a great while that were never modified.  I HIGHLY recommend this fix be done; even if you have not yet experienced any problems.

    After the /5, the starter circuitry was changed, the anti-start function in the /5 was eliminated.  In the later models the relay is used strictly as a low power relay to drive the starter motor solenoid.  Later models had a neutral switch that did more than illuminate a lamp, and BMW added starting complexities tied to that later neutral switch and also added a clutch switch on the handlebars that tied into the new circuitry.  There are variations on the actual circuitry used on the later models.  In any discussion that follows for the bikes after the /5, it is assumed that the KILL SWITCH is in the RUN position.  If it is not, no power goes to the starter relay engaging circuitry.   After the /5, the starter relay circuitry is arranged such that the starter cannot be engaged if the bike is in a gear and the clutch lever is out.   
NOTE:  it is possible to use a common ordinary auto-parts store relay to substitute for the /5 starter relay, if you understand what to do....the anti-start function is gone, however....but the /5 will operate like the later bikes (but no special neutral switch nor clutch switch functions...see below).

The starter relay on the /6 and later can be substituted by commonly available relays, but some relays in the BMW have a diode, so I don't recommend this unless you understand what is going on with YOUR relay and bike.  Use of the proper BMW relay allows the proper function of the neutral lamp.   The starter relay is usually repairable.  

***BMW never explained the real purpose of ONE of the diodes in late model starter relays.  It is my belief that the current drain and other characteristics of the Valeo starter and its solenoid switch, are such that REVERSE current effects upon the DE-energization of the PULL-IN coil of the Solenoid, are such that the starter relay points could be damaged, and the diode prevents that.

Versatile relays that can work fine for most functions in your motorcycle, such as switching lamps, running horns, starting, etc., is the Bosch (now Tyco) 330-073, rated at 30/40 amperes and 12 volts, SPDT, 5 pin, with tab for screw (tab area can be removed); or the Blazer DF005 or DF005W which also has a tab/screw mounting.

NOTE that the position of the starter relay varies by model and year.  Rather than make a listing of all the variations, here is a simple way of determining which is the starter relay (there are other ways).   If the right side of the top frame tube has TWO relays side by side (left to right) at the rearmost, then the starter relay is the one closest to the tube, and the headlight relay is the one to its right.  If the top frame tube has ONE relay at the rear most, then that relay is the headlight relay and the relay in front of it is the flasher, and the relay to the right of the flasher is the starter relay.

***NOTE!:   There is a peculiarity of the starter relay on the /6 and later models.   I think it was done for some sort of electrical disconnect function during factory checkout following production of the motorcycle.  The starter relay, under the tank (but can now be in several positions on either side of the frame backbone), has been known to get corroded male-female plug-in connections.  The peculiarity is that 100% of all electrical energy for the motorcycle (except for the large gauge wire that feeds the starter motor solenoid/starter motor) goes through a JUMPER built INSIDE the starter relay.  You can loose part or all of the electrical energy for the bike if there is corrosion at the relay or its socket.  Wiggling the relay or unplugging and re-plugging it will usually return power.  To fix properly, clean the male and female spades carefully, and THEN add silicone grease; or, a high quality protectant from such as CAIG Labs; before pushing the relay back into its socket.  NOTE that if the starter relay is warped by using excessive force during removal, it may twist the relay internal parts just enough to actually close the internal relay contacts, and fire up the starter motor!

Here is another way of stating some of this...and more...

Beginning with the /6 airheads, BMW changed the wiring at the starter relay.   There are two wires leading from the battery + terminal into the airhead electrical system.  The big heavy gauge wire goes from the battery + terminal directly to the starter solenoid on the starter motor assembly.   That supplies the very large current demand when the starter is operated.  The alternator diode board also output feeds that point.   The starter can not operate from just that wire, it needs its solenoid energized, which is done via the starter relay.     A smaller gauge red wire at the battery + terminal goes to the starter relay under the gas tank.  Do not mistake that wire for a possible third wire to an accessory socket or other added accessories.      That smaller gauge red wire, that connects to the starter relay, connects to one of that relay's internal contacts, supplying power to the starter solenoid via its mating contact, when you press the starter button (key switch on).  But, there are one or two other red wires at the relay.  Usually two heavy gauge red wires and one lighter gauge red wire are what is seen at the relay plug.  There is no connection between the two larger gauge of the three red wires at the relay socket, unless the relay is plugged-in.  The relay does NOT have to be energized by the starter button for is a design feature of the relay, metal is molded into the relay base, that jumpers one terminal 87 to another terminal 87.  There are some minor variations over the years and models, but this is basically what happens to the two larger gauge red wires at that relay....they are connected when the relay is plugged-in.  My suspicion is that BMW did this for some production line purpose.     If corrosion or poor contacts are present at the plug/relay terminals, there will be some voltage drop at those connections.  It HAS happened that a total electrical failure has occurred from such corrosion.    In the past, as above,  I have recommended that the relay be at least plugged in and unplugged, several times, and silicone-greased on the connections to help with some weather protection.  Other recommendations from me have included doing a painstaking cleaning of the contacts.  "Painstaking" because the female socket connections are hard to clean.
    My thinking changed some years ago on this subject.   As the Airheads age, more and more electrical problems are being seen from years of exposure to atmospheric smog, etc.        I now think that all the Starter Relay RED wires should be joined, permanently the next time the tank is off.   For safety, you must disconnect the wires at the battery negative first.    To do this wire joining, use a sharp Xacto knife, and using the knife blade on a rather flat angle, remove about half an inch of insulation from each of the red wires close to the relay plug....opposite each other.  DO NOT nick the the insulation without nicking the copper wires is not as easy as it sounds.    The wires are hopefully still shiny copper, otherwise you must abrade/clean them.  Find an old piece of CLEAN and SHINY stranded wire around the garage, remove the insulation, and wrap the shiny copper wires around the two or three bared wire areas, to join them tightly.  Use a soldering iron with a decent size fairly large tip to carry the heat well, and use 60-40 electronics type solder, multi-core type (or a tad of soldering rosin) and solder the connection neatly and thoroughly.  Tape up the connection properly.   Do NOT fail to do a neat job!!!     NOTE:   If your system was somewhat corroded, even invisibly, this modification MIGHT cause the charging system to INcrease its voltage to the battery; improving performance, so do check it with a digital meter in the usual fashion, after the battery is fully charged from riding or a charger, at a goodly rpm.  Check the voltage AT the battery POSTS, themselves.  I mention this because if you already have your voltage regulator adjusted to the high end of specifications with slightly poor connections (at the relay socket), you might have to make a small downward adjustment.

****On early Airheads, the starter relay & the horn relay look nearly identical, except for the
      numbers on them, & the BMW parts numbers (usually not on them).
      If the relays are reversed, the bike likely will not start, AND, the battery will slowly run down.
      The starter relay is BMW part 61-31-1-243-207; the part will have the Bosch number on it,
       0 332 014 118.
      The horn relay is BMW part 61-31-1-354-393; the part will have the Bosch number on it,
       0 332 014 406.

**** When you install a Valeo starter in a bike that came originally with a Bosch, there can be problems
       with the stock starter relay.  The problem occurs, or can, because the motorcycles AFTER 1984 had a
       weaker starter relay.  Thus, the contacts could weld, etc.  The updated relay has a stiffer springs,
       contacts that handle the increased current flow of the SOLENOID of the Valeo, ETC. ONLY the later
       model Airheads with starter relays containing a diode are affected.  See the next paragraph.

Some later model Airheads use a starter relay with a diode inside.  Some have substituted a
       0-332-014-118 relay (03-32-014-118), and some HAVE used a DF005 'Blazer' relay from AutoZone
       stores (which has two 87 terminals and no 87a terminal).  The Bosch starter relay uses two #87
       terminals, and may sub to Bosch 03 32 019 150 for 1977+ bikes.  That is a common Bosch
       accessory use relay.  Connector, if you need one, is 0 334 485 007, while the spring loaded
       terminals are 1 901 355 917.  It is certainly possible to substitute almost any common 20 or 30
       ampere 12 volt relay for the starter relay on Airheads, but there are some complications, such as
       with the /5; and with late models with diodes in the relay, so ask ON THE AIRHEADS LIST about it. 
       Complications, if any, are rather easy to deal with, so don't be discouraged with my remarks here.
       BMW has an SI on retrofitting the Valeo starter to certain bikes that came with Bosch starters
       (1985-1988 bikes).  BMW thinks that the old starter relay contacts are not up to the larger current
       draw of the Valeo SOLENOID COIL.  It is my belief that the original relay will almost always be OK,
       but if you want to install one with larger current capacity, see this document, which I have here in
       pdf format for you: Valeo Starter-2383.pdf         
OR, install a common relay as a paragraph above.

Note what I said, earlier: 
***BMW never explained the real purpose of ONE of the diodes in late model starter relays. 
It is my belief that the current drain and other characteristics of the Valeo starter and its solenoid switch, are such
that REVERSE current effects upon the DE-energization of the PULL-IN coil of the Solenoid, are such that the starter
relay points could be damaged, and the diode prevents that.

That article ALSO contains a very complete description of the starter circuitry on all BMW bikes. See also, 4. D.  below; and, 5. below.

4.  Various problems, descriptions, etc., for 'funny things' with neutral lights, clutch switch functions; etc.
      Pesky Diode Problems!!

     A. This applies to models after the /5, that have a neutral light ON when the transmission is in any gear,
          and that light is OFF in neutral.   A common cause is poor contacts in the umbilical cable plug that
          fits into the back of the instrument pod.  Clean them.   Just why this can happen, which is fairly rare,
          is unimportant to try to explain here.  If you have installed the WRONG transmission-mounted
          neutral switch, that is another possibility


Models from 1974 through 1984 (except the R45 and R65 & Monolever bikes).....have a diode mounted on the UNDERSIDE of the board inside the headlight shell.

PRE-1981 R45 and R65 have this diode plugged into the wiring below the starter relay.

On Monolever bikes, the diode is INside the starter relay (do NOT install wrong type of relay!)

   Symptoms of a shorted diode in those places:
       Pulling the clutch lever towards the handlebars will
       cause the neutral lamp to illuminate. 
   Symptoms of an open diode in those places:
       The starter motor will not operate if the transmission is 
       in neutral.

The diode must, in some conditions, pass the starter relay coil current; and absorb any high-voltage ‘kickback’ from that starter relay coil. 

I recommend a diode rated at 400 volts or higher; and at 3 amperes. 3 ampere diodes have considerably more reliability in this usage, than 1, 2, or even 2-1/2 amp diodes, due to the internal construction of the diode. Be SURE to install the new diode so that the band-marked end (silver stripe) is in the original direction. I have seen these diodes installed wrongly, that is, backwards. For the diode when mounted on the underside of headlight bucket wiring board, the banded-end (silver stripe) of the diode is connected to terminal LKK.

A different way of discussing all this follows, just below.

Read #5, below.

On a /6 and later bike, if the neutral lamp seems to function normally for neutral and normally for
          any gear other than neutral...BUT...if you are in any gear, and the neutral lamp comes on when the
          clutch bar lever is pulled backwards,
then a diode has shorted.    If that diode opens, there will be
          no starting in neutral, UNLESS the bar clutch lever is pulled back. 

          Turn on the ignition at the key switch and have the emergency kill switch in the RUN position. Put
           transmission in NEUTRAL (be SURE it is!)
.  The starter should work from the push switch.   This
           tests the starter relay, starter solenoid, neutral switch at the transmission underside, and handlebar
           push switch.

          Turn off the ignition, then turn it back on.  Put your Airhead into ANY gear (be sure it is in a gear!).
    Now, pull back the clutch lever on the left handlebar, and while pulled back, check that the starter
           button will, again, cause the starter to operate.  This adds the testing of the switch at the clutch
           lever at the handlebars. 
           To finish the testing, repeat the above paragraph, but the clutch lever should be OUT.  Hold the
           brake. Tap the starter button, it should NOT work.

           Will the bike start if you pull in the clutch lever, but the NEUTRAL LAMP lights up as you pull in the
           clutch lever?     If SO, the diode is SHORTED.  If that diode opens, there will be no starting in
           neutral, UNLESS the bar clutch lever is pulled back. 

           The purpose of this diode is to prevent  the neutral light from being on when in a gear and the
            clutch is pulled in.  

       If the neutral light is ON, and it is not the diode or switch on the bars that is at fault,
                      perhaps you simply installed the wrong switch at the transmission!  Yes, there are
                      two different switches, they work opposite to each other. See:


READ SECTION D below, for more information!!!

     C.  There is a peculiarity with the 1978-80 models, which have a master cylinder under the fuel
           tank (ATE brakes).  These incorporate a float switch, whose purpose is to illuminate the
           brake failure light if the fluid runs low.  The lamp gets tested each time you start the bike,
           via a diodeIf the diode shorts, and you are also low on fluid, the starter could theoretically
    The anode of the diode connects to the brake switch and the cathode of the
           diode connects to terminal 85 on the board and also to the starter relay coil.  The 1977
           bikes do not have the diode in the brake warning lamp circuit.  

           NOTE, as always, that  BMW's production year is not from January 1st to Dec 31st,
           because the factory shuts down in September for the annual vacation, and all bikes
           manufactured afterwards are the following year's bikes.   This was just about universally
           true for the Airheads, with a few later peculiarities (and the K bikes in mid-1992 were ID'd
           officially as 1993 models...blah blah).

     D.  The starter circuits vary with year and model. In ALL models, the starter solenoid, a huge
           relay-switch itself, is wired directly via a BIG wire to the Battery + terminal. A much smaller
           'starter-relay' is under the tank; the purpose of the small starter relay is to allow a small switch,
           the on-bars push-button, to operate a huge powerful and current demanding relay (the solenoid
           relay), via the starter relay contacts. There are differences in the various airheads are in how the
           starter relay and its circuitry are connected and wired.  These differences can be important if you
           have a problem.

           In a /6, assuming it is stock, the power to run the starter relay begins at the battery + terminal,
           goes to the ignition switch, then to the KILL switch on the bars, and then to TWO different but
           somewhat connected circuits.  The #1 circuit is the starter relay COIL + side.  The + power goes
           clutch switch, to ground (assuming the switch is functional, shorted, by the lever at the bars being
           pulled backwards).  This is why a bike should always start if the clutch lever is pulled backwards.
           If a bike does not have any starter function at that time, then the bars clutch switch or connections
           are faulty.  

           The #2 circuit is actually TWO parts:
                part a:  the neutral indicator green lamp portion.  There is another connection from the + output
                   of that above mentioned KILL switch. This connection goes to the neutral lamp.  The lamp's
                   other side goes to the neutral switch.  Anytime the ignition and KILL switch are in the ON
                   and RUN positions, and the neutral switch CLOSED (which it is supposed to be, in the N
                   position ONLY of the transmission), the lamp lights up.  
                part b:  This is a bit complicated, so follow through with me here.   I previously explained that
                   the power went through the starter relay coil and  then to the clutch switch.  At the clutch
                   switch connection (or, - side of the relay coil, which is the same thing), a diode is connected. 
                   That diode is connected to the transmission neutral switch. The actual purpose of the diode is
                   to BLOCK flow of current from the N indicator lamp to the clutch switch.  You don't want the
                   lamp turning on just because you are pulling in the clutch, rather, you want the lamp on only in
                   neutral. A diode is a one-way device when it works correctly.
                   TWO things happen if this diode fails.  If it "opens", then the neutral switch has no effect on
                   starter operation, and the neutral switch does NOTHING but illuminate the lamp in neutral.
                   There will be NO starter motor operation withOUT the clutch pulled in.  The bike is supposed
                   to be startable in any gear, or neutral, if the clutch is pulled in, and is supposed to be
                   startable anytime the transmission is in neutral.  If the diode shorts, the neutral lamp will
                   illuminate EVERY time the clutch lever is pulled backwards.  The bike will also start in neutral.
                         NOTE THOSE SYMPTOMS.

           I will ASSUME that you have a failed diode from whatever the fault indication is.  What to do?  The
           diode on a /6 bike should be located UNDERNEATH the circuit board in the headlight shell.  It is not
           easy to get to.  If shorted, it MUST be disconnected, although you can install the new diode above
           the board. What type of diode?
           You can use just about any silicon power diode rated at 1 ampere, but I prefer to use one rated at
           3 amperes.  Any voltage rating on the diode is acceptable, as they are not made in under 50
           volts.    A diode rated at 50, 100, 200, 400, or even 1000 volts, is perfectly acceptable.  Radio
           Shack sells diodes in small packages of 2 or 4 rather cheaply.   Keep the other diode(s) to
           experiment with; perhaps on your ohmmeter, to see how it tests diodes. You MUST install the
           new diode with the LINE marking on one end of the diode in the SAME direction/position as
           originally installed. You won't burn anything out if you do not, but the proper functions will not be
           had.  The line is officially called the 'cathode'.  Once in awhile diodes come with the line and an
           arrow pointing and touching it.  
           Be sure to read #5 below!

           Nerdy comment:    + current applied to the NON-line end, will go THROUGH the diode, but not if
           the applied current was negative to the NON-line end.

5.   In the 1985 and later (but NOT including the GS and the 1985 R65), the starter BUTTON and starter relay
COIL circuitry were CHANGED.   That starter relay (under the fuel tank, along the backbone) now contains
the diode mentioned in #4 above.  The starter button is on the PLUS (+)  side of the relay coil instead of the
minus side. Thus, BMW could now mount the diode INside the relay.   This can make a difference in troubleshooting!   

      NOTE that the position of the starter relay varies by model and year.  Rather than make a listing of all
     the variations, here is a simple way of determining which is the starter relay (there are other ways). If
     the right side of the top frame tube has TWO relays side by side (left to right) at the rearmost, then the
     starter relay is the one closest to the tube, and the headlight relay is the one to its right.  If the top
     frame tube has ONE relay at the rear most, then that relay is the headlight relay and the relay in front
     of it is the turn signal flasher, and the relay to the right of the flasher is the starter relay.

      Here is a circuit description for these later models, since the basic operation is somewhat similar, no
      matter the circuitry:  
      When you turn on your ignition switch, the battery positive (+) is connected to both the neutral light and
      to the starter button.  In order for the starter to operate, that starter button then sends, if pressed,
      voltage to the starter relay coil. The other side of that relay coil DOES NOT go directly to ground. 
      Rather, it connects to TWO places. It connects to the CLUTCH switch (at the lever at the bars).
      applies to earlier models too!....if they have that switch.

      It connects through the diode (inside of the starter relay) to the NEUTRAL switch (underside of the
      transmission). BOTH of these two switches, other pole, connect to ground. Thus, if EITHER the clutch
      switch or neutral switch are grounded, the button will operate the starter (starter relay will send power
      to the solenoid on the starter motor, and activate it).    
NOTE:  if you try to substitute a relay without
      the diode, things won't work as intended!

      NOTE:  The neutral LAMP is wired such that it will ONLY turn on if the NEUTRAL switch is closed
                   (shorted contacts, internally, due to the transmission being in neutral).

      IF the diode fails by OPENING, then the neutral switch will still operate the neutral LAMP OK, but you
      CANNOT operate the starter UNLESS the clutch is pulled in.

      IF your neutral lamp itself is OK, and if the circuitry to the lamp is OK, but the LAMP is NOT being
      turned on and off by the transmission being in neutral or not...then the transmission neutral switch is
      faulty. Easy to determine, just short across or open the connections at the switch on the bottom of the
      transmission. Typically with a faulty switch the bike will NOT be startable, unless the clutch is pulled.
      Thus you need to determine if the lamp is operating normally, in order to decide if you have a bad
      neutral switch, or a bad diode. Be advised that you might simply have a wire pulled off the neutral
      switch.  The neutral switches are NOT the same, early and late model...they LOOK somewhat the
      same, but a change was made in 1976.   If you have a bad one, be SURE to get the correct one.   If
      you have a 4 speed transmission, the neutral switch only activates a lamp.  On the 5 speed, neutral
      switch functions are more complex, and quite complex on later models.  Shift-kit transmissions use the
      later type switch.  
The 1974-5 neutral switches have a shorter stem.  If you install the
      wrong switch, things do not work correctly!    Neutral switches are CLOSED in
      neutral, turning on the green neutral lamp, enabling the starter function if the
      starter button is pressed.   But if the diode shorts, then the lamp is ON if the
      lever at the bars is pulled.

     If you do not install the correct starter relay, you can have an open diode indication, as relays you might
     find someplace other than the BMW bike dealer, will not have the diode.    This can happen if
     someone swapped with the headlight relay, it is not the same relay internally. 

     If you have a 1987+ Monolever bike and the lights come on with the starter in operation, there is a
     faulty diode inside the starter relay (2 diodes are in these models, inside the relay box).  This lights-on
     thing will then also happen in the PARKING lights position.

     There is an additional problem if you substitute the starter relay that requires 2 diodes, with one that
     has one diode.   You can also have the problem of the engine not wanting to turn off!

     NOTE!     There is a peculiarity with the 1978-80 models, which have a master
     cylinder under the fuel tank.  These incorporate a float switch, whose purpose is
     to illuminate the brake failure light if the fluid runs low.  The lamp gets tested
     each time you start the bike, via a diode.  If the diode shorts, and you are also low
     on fluid, the starter could theoretically energize.  See 4.C, above

    NOTE!.....a neutral switch and neutral switch diode are not the only things that
    can make the neutral light go ON when NOT in neutral....although they are prime

6.  Headlight relay......and Load Shed (Load Relief) Relay....all about them!

    The Load Shed, or Load Relief relay, does a LOT more, in the bikes with it, than in the bikes with the
    headlight relay. BMW incorporated the Load Relief relay into all bikes eventually.

    Some background first.
    Headlight relays were not used on all models, and there was none up until 1975.  From 1975 to 1977
    the headlight relay was added, and it was purely a headlight relay, used THEN to reduce current
    through the headlight switch.  AFTER 1977, the relay was kept, but had an entirely different function. 
    It was a load-shedding function. After 1977, the headlight relay is so wired that when the starter motor
    is energized the headlight relay coil de-energizes and relay contacts OPEN, and the headlight goes
    OFF during cranking.    At the same time, 1978,  BMW eliminated the light switch. Thus, same relay,
    different functions.

    The headlight relay on 1978+ models has a diode between connection #86, the green or green/violet
    wire, and connection 87b, the gray wire. The CATHODE of the diode connects to 87b.  This diode
    sustains the tail and instrument lamps DURING starting...probably a German safety requirement. If the
    diode shorts, the ignition will stay on, and even the key will not shut off the engine, unless you
    disconnect a battery wire...which removes the relay circuit problem instantly...but only until the
    next start.
     Pin 85, the black wire, is the "to-be-grounded" side of this relay's coil, & connects to the
    STARTER MOTOR. During cranking, BOTH sides of the relay coil connect to the nominal 12 volts, & the
    relay is NOT energized. Because of this CLEVER idea, a problem with an open starter motor, which can
    be intermittently open, can cause this relay to be inoperative! Thus, no headlight unless you use the high
    beam "passing" push button, which bypasses the has its own separate wiring.   NOTE!  This
    PASSING switch that turns on the high beam, is spring loaded to return when you remove your finger,
    AND it bypasses the headlight relay, AND it is also NOT fused!     THUS if you have a problem of NO
    headlight in High or Low beam selection switch setting, but you push that switch all the way down, for
    passing mode, and the headlight comes on, check the headlight relay. 

    Here is a different way to approach to explaining how the headlight relay works (this applies to
    /6 and later models but not the 1975-1977 models):
The headlight relay is not what you may think it is.  The headlight relay is NOT a relay that simply
    selects between high and low beams.  In fact, it does not do that at all!  The purpose of the headlight
    relay is to turn off the headlight when the engine is being cranked by the starter motor.  The coil of the
    relay is so wired that one side goes to power, the other side to the starter motor.  When the starter
    motor is NOT energized, the relay is ON (assuming ignition is ON), and the lights operate normally. 
    When the starter is energized, the headlight relay's coil has battery voltage at BOTH coil wires, so the
    relay turns OFF.  That turns off the headlight.   But, a DIODE built into the relay, keeps the tail light &
    the instrument lights ON during cranking. The BARS hi/lo switch passes full current to the headlight
    directly.  THAT is why a relay should be added if larger than stock headlamps are being used.  The
    Eastern Beaver relay kit is very convenient for this, as it is plug and play (except to install a red fused
    wire to the battery).  NOTE AGAIN: The High Beam Flasher part of the bars switch is a separate circuit
    to the high beam. 

     If the relay is marked 1.244.411 then it has TWO diodes inside.  I am not 100% certain of the
     extra diode's function.   I THINK that the extra diode's function is to prevent current in the
     opposing direction from operating the relay.  That could come about with a stuck starter
     solenoid (which contains two contacts).     This other diode is connected so that the cathode
     connects to pin 85, and the anode is to the coil.  From 1987, Monolever bikes had two diodes
     diodes in that relay.  If the lights all come on when the starter is operated .... or Park position
     of the switch is selected.... then one of those two diodes has shorted.

    The method of de-energizing for the headlight relay from 1978 is that the starter is at + 12 volts when
    cranking, and so is the input side of the headlight relay coil; but the coil is also connected to the
    starter... so with the same voltage on both sides, the relay coil is NOT energized.  The headlight relay
    coil is energized all the time normally when the key is ignition-on, except in cranking. There are normally
    closed and open contacts inside that relay, and the appropriate ones are used for the functions
    intended, which include the headlight lamp, but BMW wanted the tail light and instrument lights left ON
    during cranking, so that require the other connections inside the relay can.

    The headlight relay is wired to the headlight switch and momentary Hi Beam switch, depending on
    model and year, and is not wired the same for all models and years, and further not the same on even
    the same model in the same year as shipped to the same country!!! I've run into this, and found new
    wire colors not on schematics....and combination of Euro and USA...ALSO!!! One example of the result
    is that on some Airheads, the Hi beam flasher button will operate withOUT the key being on.

    The Load Shed relay, in the later bikes, is for the same idea....but the Load Shed (Load Relief)
     relay works with many more items.
 For instance, the Load Shed relay may, during cranking,
     DE-energize the horn, the turn signal flasher, the right bars switch assembly, and the heated grips, if
     any.  Further, there are differences between Euro and USA bikes in the Load Shed circuit, and the
     circuit may actually be split into two sections, one of which is fused. I think I remember the R100GS
     using Fuse #4 for that.  Note that the effective operation of the Load Shed relay is quite similar to the
     headlight relay....but with added items being shed of power during cranking....and in some instances
     with the key off.

All these headlight relay and load shed relay circuit changes are confusing.....the complexity
    has foiled many an owner in trying to identify a problem.

    Now, my opinion.   The headlight draws roughly 55 watts on low beam. Actually, that is the rating, the
    actual drain with losses in wiring, switches, etc., brings it to a bit under 50. At about 12.5 volts, and ~55
    watts, the current drain is only 4.4 amperes. That is hardly much, compared to the starter motor, which
    draws as much as 100 (or even more amperes on a cold day cold start). Even if you add heated
    grips, the amount is low. Thus, to MY way of thinking, the complexity of the headlight relay or load shed
    relay was not worth BMW's efforts (there is a reason for it for ABS bikes, but could be done MUCH
    more simply), and complexity.......and, in particular, the peculiarity of how BMW de-energized the relay
    (by wiring it to the STARTER, so the starter is the normal GROUND for the relay coil).  If you think
    about all this, you may get the idea that if the starter motor has a lot of carbon brush dust in it, that
    peculiar things can happen, depending on the particular'd be correct.  Just in case someone
    who really knows the circuitry wants to send me commentary, yes, I am aware that some of the bikes
    don't shed the loads in the exact way I am describing.

    BMW makes complicated vehicle electrics. BMW has a hazard light system that was available on some
    bikes, and as an add-on is a complicated MESS.  I have those schematics on this website for
    anyone wanting to look at them, but it surely is WAY over-complicated. Sometimes I think BMW has a
    round-table discussion with sales...[ and engineers (???)].....and the discussion is "no matter how
    complicated it gets, what would you like to see in electrical functions....?".

    BMW is noted for complex electrical things. The first time I delved deeply into a K bike turn signal
    circuit, and the MESS that BMW has to monitor certain lamps, and shut off some lamps after so many
    feet or so many seconds,......... gads!  One of these was so complex that I wrote an article on it to help
    those having problems.  Just to be a bit more fair, here, some of the complexity comes from Euro
    safety requirements.

    My thinking is, and I have so-advised those doing 'café' conversions, is to eliminate the headlight relay
    and starter motor connection hassles....and a few other things.  I am NOT recommending anyone
    modify the stock system or remove it on anything but a Café type bike, which usually does not have the
    stock type instrument pod, etc.   The stock setup works fine.....until it doesn't. Then you get to figure it
    out, ask the LIST perhaps, and still go nuts(?).  If you think BMW is the only company having
    complex electrical's, think again.......all vehicles do, and have for some time.

ASIDE NOTE:    If you have the folding-out fog/driving lamps in your fairings in place of the air vents, there is a diode associated with them, and you might want to read the notes here:

7. The charging lamp (GEN) MUST be brightly lighted when the ignition is on, engine not running. This lamp provides the initial alternator rotor energizing current. DO NOT depend on the alternator to self-energize at 5000 + rpm.   IF the lamp goes out when the engine is running (especially at say over 1500 rpm)...but there is no substantial charging, the regulator can be checked with a little jumper wire with spades attached...see at the top of this article.   Remove the tank, UNplug the voltage regulator, and jumper D+ blue to DF black in the plug.  DO NOT jumper to a brown wire!!   The proper jumpering bypasses the regulator, and the light should go out around 1000 to 2000 rpm.  Strong charging as rpm rises indicates a bad voltage regulator. If the lamp was not lit at any time, and the lamp itself and its printed circuit connection (and no hidden cracks!) tested OK, and if the regulator was bypassed by the jumper, and the lamp now lights up, you probably had a faulty regulator.  If you need to delve further, you might start by measuring the voltage at the rotor terminal...or, better yet, the slip ring itself (brushes have been known to not make contact!).   BTW: If you have a bad regulator, you can limp home at lower than normal rpm (to avoid overcharging the battery), with the jumper in place.   Most any three terminal regulator used in modern cars also works.  
NOTE: After the /5 (rotors about 7 to 8 ohms), rotors measure about 3 to 4 ohms, and about 2.7-3 for the last production.   If your rotor measures many tens or higher, the rotor IS BAD (be sure it is not bad brush contacts...measure AT the slip rings, then at the brushes).  The brushes typically add about an ohm to the rotor reading.  Rotors tend to OPEN circuit, sometimes this happens only at some rpm, or when hot or cold.  When a snail spring bottoms-out, the brushes get intermittent.  If the snail spring has insufficient pressure, there will be poor contact of the brushes...particularly important on the later rotors.    There is information on this site on problems with the diode board connections that can influence charging from tiny voltage drops:
Information on modifying the GEN lamp circuit so that the alternator will still operate if the lamp burns out, is filed elsewhere's on this site:


8. If you have a GEN lamp that lights up faintly while riding along (sometimes it is faint enough to be seen only at night)...  this is almost always due to a build up of small amounts of poor contacts and/or corrosion, at various places in the electrical system. It IS POSSIBLE for a badly sulfated battery, with one or more shorted, or nearly so cells, to cause the GEN lamp to come on, often dimly.  Electrical connections can cause that dim lamp, as can some brush problems. If this gets bad enough for the light to shine fairly good, you have serious connection problems OR possibly so-so brush contacting of the slip rings.   Brushes USUALLY last about 70-80K. They will last less on bikes ridden in dirty air or with higher electrical loads. Brushes are best changed with the stator assembly removed.    NOTE that when at least one brush is worn far enough its snail spring will start to bottom out on the plastic brush housing.  At that point, a tiny bit of wobble (slip ring runout) of the rotor will cause the GEN lamp to light up dimly...and possibly to increase that brightness as rpm is raised. 
There is an article on this website:

Note 1:  When a GEN lamp does NOT light up at ignition key turn-on & engine not running (or at idle rpm), the lamp is faulty, or the lamp socket, wiring, regulator, brushes, or rotor is open circuited.  This is almost always very easy to figure out.
Note 2:  The GEN lamp is connected at the output of some small diodes in the diode board, and the other side of the lamp connects to the battery, but through the key switch.  As the alternator begins to produce current, those small diodes are SUPPOSED to have the same exact output voltage as the large power diodes that feed the battery more directly.  Anything in either of these two connections circuits that allows for enough voltage difference to light the lamp will do so.  Thus, a difference could occur with a problem in the diode board, but also in any voltage drop that was excessive at several places, including the switch, the starter relay jumpering, etc.  It is actually possible to measure the voltage drop down the system, by using a simple setup.  You connect your digital meter positive (red or + ) lead to the battery + terminal, and the meter negative lead connects to various test points you  are interested in.  That allows directly measuring the drop itself.  Be SURE the battery connections are very good, a KNOWN GOOD battery, and connections from battery to transmission and to the starter motor and to the large terminal on the right side of the diode board, facing from the front.  A known good battery is NOT just one that will start the bike.  You can measure the battery terminal voltage, under load, such as the headlight or during starting, that will give you some idea.

.Alternator brushes are about 16-1/2 mm long when new, measured from the middle of the concave to the top of the brush.  While there have been minor changes in the brush holders over the years, a common problem is to let those brushes get too short, and then the coiled spring on the brush will bottom out on the brush holder, the brush will then have no, or hardly any, pressure against the rotor, and you will have strange charging problems. This includes often a glow from the GEN lamp, at riding speeds at night, sometimes even visible in daytime.  Note that the rotor is not perfectly concentric in operation, thus as it rotates at various rpm, it can cause the brushes to bounce when they are very short and the snail spring is touching the holder.  This can make for a brightening or other irregularity of the lamp as rpm rises.   It is best to replace the brushes when they are around half worn, but you can let them go until the snail is almost bottoming.
  Do NOT clean the slip rings, which are soft copper, with abrasives.   A pink lead pencil type eraser is OK.  Use of fine grade kitchen cleaning sponge/plastic light scouring pad, is OK...NOT the heavy duty type.  Carbon on the slip rings does not hurt, so a bit of most any drying solvent and a rag is enough cleaning.    Cleaning any excess carbon from the brushholder outsides is a GOOD idea.   
If you have to remove and replace a rotor, heed this warning!...USE ONLY the factory tool, or a homemade tool of HARDENED steel.  Do NOT use soft steel.   Information on making a tool is on the website.  The BMW factory tool is not expensive, and a good idea for one of these tools to be in your on-bike tool kit!

Brushes connect to terminals with casting stamping identification of D- and DF.  D- is the grounded terminal, even though it appears insulated.  Df is insulated (be sure you do not mix-up the insulating washers during brush replacements), and D- must go to the BROWN wire.  Do NOT goof....many have! NOT fail to properly assemble the white plastic brush holder insulating washers at the correct Df terminal...IF you have disassembled this area.  If you mix them up, you will ground the Df wire, the D- wire is grounded elsewhere' the GEN lamp will light up, but you get no charging!

NOTE:  When brushes get worn enough, and the snail spring will touch its own side-notch in the white plastic brush holder, and even very slight and acceptable run-out (wobble) on the rotor can cause intermittent contacting of the brushes.   This can vary with rpm, making you think that you have a rotor that might be opening at higher rpm.    

9A. If you have to remove a diode board, when replacing it, note that the black wire goes to the starter solenoid, and the blue wire goes to either of the D+ terminals (one D+ terminal is not used).   Alternator STATOR housings have three terminals next to each other, the three mating wires may go to them in any order.  They MUST fit tightly.  A /6 and later diode board has an extra terminal on the left side, and a wire from that terminal goes to a terminal on the stator housing.   Diode boards of all models can interchange, but a /5 board will give slightly lower charging in a /6 system. 

9B. A very rare situation is for the voltage at the battery to be WAY excessively high while riding your Airhead down the road.  This condition can come from a battery that has high internal resistance and/or poor grounding or other connections to the battery.  It can come from a bad voltage regulator.  It can come from a bad ground (brown wire) coming from the voltage regulator socket. That wire MUST be grounded.   Another possible cause is a bad SMALL diode in the diode board.

10.   The headlight shell may contain a parking light lamp socket that may be unused....such as on RS and RT models.  I am NOT talking about the separate eyebrow lamp!   A 10 or 20 watt quartz lamp can be installed at this unused lamp socket.  Phillips bulb 12452 is a 10 watt quartz, has PLENTY of light output.  The stock lamp in those sockets, when being used, was only 4 watts.  The 10 watt quartz can be used instead of the headlamp, saving some power.  

Although I do NOT recommend it, if you are installing an oversize headlight lamp on a /6 or later (the /5 already has a high temperature lamp socket), you should install a high temperature socket for the lamp.
Here is ONE source; scan down this page to find the ceramic one:

11.  The early spark plug caps were 1000 or 1200 ohms, not the later 5000. It really does not USUALLY make a difference on a stock 1980 and earlier points bike if you use 5000, but 1000/1200 caps MAY give slightly better performance if  other things are marginal.  NGK makes nice spark plug caps.  LB05F are 5000 ohms, LB01F are 1000 ohms.    Check them with a meter before purchase, be SURE they are they make similar ones that are 10,000 ohms, DO NOT use LB10F. ....and they must NOT be used.  Do NOT use anything but 5000 ohm caps on the electronic ignition models (1981+).  If you have a POINTS model, without any electronic ignition module, etc., and you are replacing the spark plug caps, use 1000 ohm.  NEVER use the carbon type of resistance wire.  I recommend AGAINST resistor spark plugs.

12.  Ignition cutout problems after some miles on the road on 1981 and later models can be due to overheating of the module under the tank.  It is NORMAL service to remove the module and clean and replace the electronic heat-sink grease every couple of years.

13.  The /5 bikes had a 180 watt alternator.  This can be updated to a specific version of the early 280 watt alternator used in 1974 and maybe early 1975.  You can identify which /6 alternator stator you are looking at, by the stator size....if the one to fit a /5, it is 105 mm; all the rest are 107 and won't fit a /5.  You can use the /6 diode board which has the Y connection diodes for the stator, or just use the /5 diode board, BUT, with a modest reduction of the 280 watts.    Later rotors and electronic regulators CAN USUALLY be used, and require no maintenance, and fit perfectly.     Bosch stators have a Bosch number on the HOUSING.  The numbers ending in -001 and -002 are the early type, and are 105 mm.  -003 is a R90S stator, and will result in slightly reduced output.  -004 and -005 are the 107 mm stators.  Rotors for the earliest bikes were 73.4 mm in diameter.  For the 1975 /6, and later, the rotors are 73.0 mm in diameter.
NOTE:  trying to use an earlier higher resistance rotor with the last generation of higher resistance STATORS is NOT a great idea.

You can get a later stator and in a kit from Motorrad Elektrik.    They also have a higher power alternator conversion for the later 107 mm stator bikes.

There is an EnduraLast permanent magnet alternator conversion kit available that will fit all models of airheads...with LOTS of wattage output.  Kits in 105 AND 107 mm are available.  

NOTE:  there is some testing that seems to show that the latest low ohm rotors do slightly better in all models for lower rpm charging.  NOTE that these lowest ohm rotors work best with the latest model VR.

NOTE:   BMW modified the stator windings and rotor resistance of the last of the Airheads, and the tradeoff was that while the TOTAL watts output was reduced some (to around 240), the charging began earlier. Due to stator changes, I cannot recommend any rotor be used with the later slightly higher ohms stator with the earlier rotors.

14.  Electronic regulators WILL substitute for the earlier mechanical regulator, the plug is the same, and it fits in the same mounting holes.  The BOSCH metal can electronic regulator, which looks like the Bosch mechanical metal can regulator, but is a bit shorter, works the best.

15. Wiring up heated grips.....and other situations, including series-parallel switching, ETC:
Typically, for heated grips, you need a method to be able to reduce the high heat that would occur with both grips having full power on them all the time.  BMW uses a resistor and a hi/lo switch.  That works OK.   Use of a power rheostat is not overly practical, as its physical size would be fairly substantial.
 In order to reduce the heat from grips, there are three 'practical' methods:
     a.   Sometimes I am asked how to wire up a single switch so that something, such as heated grips, can
           be operated, via a single switch, for both as parallel and as series connection.  Here is how to do
           that.  You need ONE switch, and the switch is called "Double Pole, Double Throw", or, commonly,
           DPDT.  The switch has 6 terminals.   You can purchase these switches  commonly in two position;
           or, three positions, the 3 position type, which I usually recommend, has the center position being
           OFF.  In that instance it is "DPDT-Center Off".   Turn the switch upside down so you have a vertical
           row of three terminals on the right, and three on the left.  The center terminal of either the left or
           the right is always the moving contact for that side.   On the LEFT side, connect the center terminal
           to +12 volts, probably via a fuse and possibly via your key switch.  Connect the UPPER terminal on
           the LEFT side to Load  #1.  Connect the CENTER terminal of the RIGHT side to this SAME upper
           left terminal.  Connect Load #2 to the lower terminal on the LEFT side.  Connect  the not yet
           connected Load #1 wire to this same point.  Connect Load #2 unconnected wire to GROUND.  The
           last connection is the LOWER one of the RIGHT switch side, ground it.   NO connection is to the
           upper right side of the switch.

           Here is this sort of thing in much much more depth, a more graphical explanation:

           Ground one side of one heated grip...let us just say this is one of the Right grip wires.  Connect the
           remaining right grip wire to one of the left grip wires.  On the switch, connect the center (arm
           internally) of one section to the +battery after the ignition switch, but via a 4 ampere fuse.  On that
           same section of switch, connect one terminal to the left grip wire that had no connection. On that
           same section of switch, connect the other terminal to the JUNCTION of the two grips wires made
           previously.  You now must wire in the second switch section. On the same end of the switch that
           connects to the ONE left grip wire, run a short jumper to the CENTER (arm) of the other switch
           section.  The same end of the switch, opposite, other section, has no connection. The remaining
           connection of the second section is connected to ground.    When switch is in center position, no
           power goes anyplace.  When switch is in one position, +12 goes to arm of first section of switch,
           then to the left grip and to the arm of the second section. +12 travels through the left grip, through
           the right grip, and then to ground. Thus, this is the LOW power, or series connection.  When the
           switch is in the other position, the first section of the switch applies +12 to the junction of the two
           grips. One grip, the Right one, then goes to ground. The other is grounded via the second section
           of the switch.

           This is a sort of  graphical view of the rear of a DPDT switch, with the O meaning a terminal, and
           my adding of alphabet letters next to each one. It is critical that the switch be wired EXACTLY as
           described below.

                    Oa Ob

                    Oc Od

                    Oe Of

Connect two grip wires together. Ground one right grip wire. No connection is made to terminal b.
Connect +12 to c, via 4 ampere fuse and to the output of the ignition switch. Connect a and d together with a jumper wire. Connect e to the junction of the grips wires previously joined.  Connect the a-d connection ALSO to the left grip wire.  Ground f and ground the Right grip.

NOTE that the wattage in a circuit follows Ohms Law.  Because of this, when grips normally in parallel mode are changed to series mode, the heat (wattage) produced, assuming both grips are identical in resistance (which they are, close enough), is reduced to a fourth of the parallel amount.  This is a low value, but may be acceptable if the parallel connection is WAY too hot...which is not at all uncommon with aftermarket heated grips.    The Law I mentioned is: voltage squared, divided by resistance, equals watts.   What this means on a practical basis, is that using the worst case (a 14 volt level whilst cruising), the power is 196 divided by the resistance.  If,,,,for just an example.....the grips are 15 ohms EACH, in normal high heat 'parallel mode', then EACH has 13 watts of heat.  If the grips are in series, then the resistances ADDS, and you have 30 ohms.  Now the heat is a TOTAL of 6.53 watts.   3-1/4th watts in each grip is kinda low, still, it is feelable....barely though.  THUS, using a series and parallel switching method is NOT what I recommend.

    b.  Heat grips are normally wired in parallel, and a switch used to turn them on and off, and a secondary, low power position is on the switch....and, in that switch position, a resistor, which is actually a wire of a special type, lowers the power to the grips, but that resistor itself can get HOT.  This actually works well.....if you like the setting of the Low position, and the wire is routed properly, or if you use a resistor it is mounted properly.  BMW basically did it when it installed the heated grips....or your dealer installed the BMW grip heating system.

     c.  This is the preferred method for some installations:  Use a small control box of the type that is used for heated clothing.   These vary, but the ones that control via pulsing or duty-cycle are the best, as they hardly get warm themselves and are very efficient.    Typically these have a type of 'transistor'  inside, that is controlled by the adjustment knob.  At a very low heat level for the clothing/grips, the transistor is turned on 100% for a fraction of a second, then turned off for a much longer period of time.  As the heat control is adjusted higher, the ratio of on to off time varies, until at full heat the clothing/grips are on all the time.   Because there is hardly any 'resistance' in the semiconductor no matter what the adjustment is set at (provided a pulse circuit is used), heat developed is quite low, and efficiency very high.   Most light dimmer controls in your household work pretty much the same way.  Basically these devices, to describe them another way, act like you are manually operating a switch, for either a short period of time, or a long period of time.  Unless you are good at electronic design work, it is better to purchase one of these little boxes.  

The cheapest way to go is the single resistor method (b.), which actually is quite decent...but you need to find the right value of resistance...and mount it in a place the heat in it is no problem.   A 6 ohm resistor was used by BMW on many models.

There is an article on this website with the schematic diagram of the factory heated grips....see

16.  Craig Vetter's Windjammer fairings have on-line help available, including the wiring diagrams, information on saddlebag and windshield mountings, etc.

17.  Any stock airhead electrical system, (including the /5  180 watt system), will maintain the battery in a charged condition, from something like 2200 certainly not over 3500 rpm....ONCE the battery is fully charged.   The later model airheads have some slightly higher power usages, and almost always will require 2800 minimum.  Adding an electric vest will raise the rpm required a bit....perhaps a FEW hundred rpm.  Continuous riding below 2800 is not good for the engine.    Any really appreciable electrical load may require 4000+ rpm, continuously.     On a practical basis, considering sometimes poorly maintained electrical systems, old components, etc., don't plan on over 80% of the rated watts output of the alternator.   Commuters (stop and go, heavy traffic) will have more problems keeping the battery charged. 

18.  Folks sometimes ask about the wiring diagrams for such as the 4 way flasher, various versions of headlight switches, and so on.    Some of this information is in some factory manuals, rarely in owners manuals to any degree, and almost nothing in such as Haynes or Clymers.   Reference can be made to information on the R65 4 way flasher (hazard flasher), which has application to other models, and on other items mentioned here in the 1985 service fiche #4, section 61.  That will also provide information on all the 1979 models for adding a headlight on off switch, applicable to others, ETC.   There are also other sources.  I have most of the information.  There is a separate article on this website for these things:

19.  The earliest /5 model was not fused.  The later /5 model fusing really should be added. Don't let  your wiring burn up! 
 Besides that, the /5 and early /6 bikes did NOT have any short circuit protection for the headlight flasher circuitry.  I recommend fuses be added ....or, at least, a fuse in the main power lead from the battery (not the starter wire though).    Just adding a fuse in the battery circuit will be of some help on any of these models, if you don't want to add the proper fuses at the proper place in the headlight shell.    The later blade type fuses are more reliable than the tubular types. 

20.  BMW has two bulletins out on certain models built from 1985 into 1989, regarding the brake light switch on the handlebar, and the switch at the rear brake lever.  The information will be found on this website at

21.  Here is the URL for the Chicago Region BMW Club, the source for their various repair manuals.
 The Electrics manual is now priced at $30,  is simply THE best electrics manual for airheads, and Oak was primarily responsible for that manual.  HIGHLY recommended.
That website, shorten the URL, also has some information on the background of that Club, and the background on Oak, etc., and those various manuals.     My CRITIQUE of the electrics manual on this site:
Once you obtain your Chitech electrics manual, use my CRITIQUE to pencil-in the corrections!

22.   The R100R models PRIOR to serial 0280227 (the last 7 characters in the VIN number) have a problem, and you should consider adding a grounding wire, on silver-painted frames models.   Failure to have this added ground wire added WILL (or MAY)... show up as misfiring...or...poor alternator output.   ADD a wire, neatly, between the left starter motor cover, and the ignition module bracket.  Use a 16 gauge or 14 gauge wire, SOLID BROWN in color, so it follows factory color coding for wiring.  You could fashion something from INside the starter area, to the cable outlet at the top of the timing chest, if you wanted it more hidden.

23.  Turn Signal Flashers/Relays:

The /5 bikes use a 2 terminal flasher relay unit.   It is load and voltage supply dependent, so flashing speed varies with alternator output (rpm), if you use different from stock recommended lamps, etc.   The following is an acceptable substitute:

   Tridon Stant Electronic Extended Life Flasher 12 Volt, 2 Terminal  EL12
   Actually, almost any of the two-terminal flashers will work OK.

After the /5, the stock and $$$ electronic flashers are a bit complicated inside; and they have a dual relay function when any of the directional signal lamps burn out.  You usually lose the special indication for a burned-out lamp, with the aftermarket flasher, but still can have the turn signal indicator lamp function like in a car, and including for a burnt out lamp. There are three different uses/types of these flashers.  On the early version flasher relays, there is a terminal 49G, which has the same function as 49a on later relays.  Early flashers had the indicator lamp on terminal C, later ones had the same type of function, but the terminal is now marked KBL.
ALL of the flashers from 1974 can be replaced very similarly with such as the Tridon EL13..or HD13....and similar.  If your motorcycle has TWO indicator lamps (one for left, one for right), then there is NO connection to "C" or "KBL", and you need NOT be concerned about making that connection when substituting an aftermarket flasher relay.

It is possible to rather easily add a piezo tone unit to any of the flasher setups.    NOTE that aftermarket flashers don't use the brown ground wire that BMW's flasher relay does.

A recently recommended substitute is the Blazer (or, Tridon/Stant) flasher.  The model used for that recommendation was 550, which is a thermal flasher, but handles the BMW lamps just fine, and would even handle extra lamps, such as on a trailer or hack.  An electronic unit could also be used. 

I recommend that for the /5 you use a thermal flasher, it is easy to connect, and for /6 and later I recommend you use the mentioned EL13 or HD13 or equivalent. There are others that are OK.

NOTE!   For those installing extra lamps, or have specific reasons to replace an existing flasher unit,....ETC.....there is a heavy duty flasher unit available at auto-parts stores, under the SignalStat brand, model 263.   Mechanical and electrical.  Flash rate is 60 to 120 per minute, has 3 each 1/4" male spades, is 1.33" round, 1.35" high, works on 11-15 volts, and from well below freezing to damned hot.  It will handle 20 ampere loads!!

Do NOT use the solid brown wire that BMW had in its connection to the original flasher relay (1974+).  Connect the old wire that went to KBL or C to the flasher P terminal.  The BMW wire for this is probably Black/White or green.   The aftermarket flasher relay probably has a terminal marked X, that goes to the +12 power, the old wire connected to flasher terminal 49, likely was green/black.   The turn signal output of the new flasher relay is L, for LOAD, and is likely green/yellow.

Connect the P (which stands for PILOT lamp) terminal to the indicator lamp (usually a green wire); the X terminal to the +12 power (old terminal 49 wire, green-black); and the L terminal to the load (old terminal 49a, green-yellow).  If you have two INDICATOR lamps, don't connect to the P terminal.

NOTE!    The early /6 bikes had poorly grounded front turn signals.  You can run into all sorts of intermittents, and strange indications from the pod turn-signal indicator lamp.  While other causes, including a bad flasher relay, poor contacts and bad lamps, etc., can cause some similar problems, DO try improving the grounding. Test for the problem, and if you have it, fashion some grounds from the headlight bucket to each turn-signal pod.  Please use conventional color code, so that means solid brown insulation.  BMW fixed the problem in ~1976.

NOTE!   Some of the flasher relays are PRICEY from BMW.  You might be able to fix yours....and here is one particular problem that is easily fixable.  This happens with
the later model bikes where the flasher relay is mounted on the backbone frame, under the fuel tank.  These models are 1981 and later GS, G/S, ST, R65LS, and, in general, all the other models from 1988. 
Here is a typical complaint and fix:
    On a recent ride, my turn signals quit…left and right no flashing, same for the lamp.
    The fix:
        Remove the fuel tank and tested the wires (by slight pulling up and down to the flasher relay socket). No problem with the factory crimping should show up. 
        Consider SLIGHT tightening of the 3 female connectors just a bit where the relay male spades fit. Use a pointy tool.  ONLY SLIGHT bending.
        You will probably find the fault is inside the relay, often (not always) you can prove it to be a SIMPLE FIX, by slightly moving the relay, left-right…just a bit of
        pressure both ways.  That MAY cause the turn signals to stop and then restart.   In most instances the problem is inside the GREEN relay made by Wehrle.
        This relay contains an integrated circuit & a small electrolytic capacitor, etc  The capacitor USUALLY dries out and causes flashing speed problems only after
        a whole lot of years, so you can probably disregard trying to test it. It is LIKELY that 1, 2, or all 3 of the relay's male spade solder joints inside are cracked.
        To get inside, you must pry at the side places with a very thin tool.  This can further damage the solder joints, but not by much, and you have to fix them anyway.
        Remove the printed circuit board with the mechanical relay, as one unit, just as built.  Mount the relay into a vice, with LIGHT pressure, so the male prongs &
        circuit board are at the proper 90 degrees, and RESOLDER the three male solder joints. Install the relay cover, being careful that the printed circuit board fits
        into the inside cover groove especially for the printed board.  Be careful to install the relay into its socket squarely, with even force on the whole case, and not
        too much force.  You just saved $$$.


The dash voltmeters (as on RS/RT)  themselves are almost always quite accurate. Usually to about as close as you can read them; but they are not connected to the battery at the battery terminals...but, much further down the line, so-to-speak. If the SYSTEM is in good condition, the dash voltmeter on a RT will read approximately 0.3 volt +- 0.1 lower than the reading taken at the battery terminals.
The problems with the readings, and wildly swinging needles,  stem from several places.
FIRST is wear and somewhat poor connections at places such as the ignition switch, connections at the starter relay (that little square relay under the tank), and in the headlight shell. When the connections get just a bit too much resistance, you may well NOT see any problems with anything but a swinging voltmeter, and they can swing wildly. I have fixed the voltmeter internals, but it is not worth all the effort to take them apart. There are some things that make the voltmeter even more wonky. The alternator stator connections may be somewhat overheated and providing iffy connection. Same for the + output (large red wire) at the left end of the stock diode board. These wires MUST fit TIGHTLY to make good connection, considering the large current flow. If the wires do not fit tightly and make good connection, the output of the alternator system will have A.C. spikes on it, plus somewhat fast happening D.C. spiking, and that WILL affect the VOLTMETER!

Damping of the voltmeters can be poor. Several reasons for that, one is that a CAR voltmeter, that looks identical, was installed. A second reason is that damping of the correct voltmeter CAN decrease, and considerably, due to aging of the internal parts. A massive capacitor external can help, but is not the best answer. A series resistor and a modest capacitor works better, but, still, I don't like that method. Another reason is that the pivot bearing of the voltmeter will age, and wear, and as it does it gets grabby, and can thereby get jumpy, and can look rather similarly to a voltmeter with bad damping.

The turn signals require about 4 amperes or so from the electrical system (2 amperes +- from each of the two lamps on either left or right sides of the bike). That electrical drain comes from close to the same place the voltmeter is connected-to. That means that the voltage to the voltmeter will have a fair change in value, and if resistances in the system are high enough, the meter can really swing A LOT! Most of the digital meters that are designed for vehicle dashboard use are damped electronically quite well, and there is a sampling rate situation going on with those digital meters that also ...USUALLY....tends to ACT as if the meter was much more highly damped. Not going to get into that further.

Unless you need absolute originality, I would suggest a 2-1/16" round DIGITAL meter, and they are available reasonably, from such as Summit Racing. You won't then need the lamp either.   For those who want a high quality totally sealed meter, and are OK with one that is a rectangular cube, the one's made by DATEL are VERY good.


VDO instruments:   It is possible to substitute VDO instruments, such as    Voltmeter:  #332-103 (or  332103).   This fits the original 2-1/16" round hole, is well-dampened, and has black face with WHITE LETTERING and red pointer, 8-16 volts.  It uses a spin-on clamp.  Has through-dial lighting; and using diffusers, can have red,  green, or white lighting.  It has a 8 to 16 volt scale, just like the original one in your Airhead.  Was MUCH cheaper than buying the BMW voltmeter from BMW.

Clock:       VDO  #370-152   Those are black face and black bezels, and have a threaded part to mount them, rather than a bracket.
                  That was discontinued, and the new number is 370-100 and 370-100B.   These are way too pricey for most to consider.

    You can also use VDO Vision Marine voltmeters and clocks.

Substituting an accurate DIGITAL meter for the existing BMW in-dash round meter...or, just adding one:

There are digital voltmeters on the market that require a separate power source. There can be problems with them! Some of these require...or MAY require, a separate supply, perhaps 9 volts.  The worst part is often that the supply negative is NOT common to the measuring side of the meter....UGGGH!       These are difficult to use, and some use them with an external small 9 volt battery.   I recommend you do NOT use this type; AND, there is NO NEED TO.  The type of digital meter I recommend you install in your bike (Airhead, K bike, ETC.) is a TWO WIRE METER.  These meters provide their own power from what they are measuring.  They need NO lamp either!  They are LOW DRAIN.   These meters are available in LED and LCD versions.  The LED version is much more visible in all conditions of lighting (day, night, etc.), and pulls only a small bit more current ...and that drain is totally negligible on your bike, if you wire it so the meter is powered AFTER the ignition switch.  Drain is UNDER 0.020 ampere for the Datel (Murata) unit...that is under 0.28 watt!  It is BRIGHT!!  There are numerous types of digital meters available.   
        a. To install a ROUND faced digital voltmeter in the Airheads, in place of the existing round voltmeter,
             I use a 2-1/16" round faced type from such as Summit Racing, in this country.   See also
   , they have BOTH round AND rectangular digital meters.
        b. To install a rectangular type digital voltmeter:  My favorite meters came from
             This is now   Good quality, rugged, reliable, accurate, red or green or
             blue digits, and work fine at any temperature. I recommend RED digits.   See also
    or   (Retail outlets primarily, Datel type meters,
             with information, so snoop around).  
 I recommend Datel's ( model number
             DMS-20PC-1-DCM-C.  These draw only about 13 ma when powered.     If you want a 
             panel bezel, the part is DMS-BZL4-C, with gasket.   The meter will read accurately from +8 to
             +50 volts D.C.     These are two wire, self-powered, need NO LAMPS.  They are encapsulated,
             in a polycarbonate case, and are VERY rugged.  RED digits for the above number.  If you want
             blue digits the number is DMS-20PC-1-DCM-B-C; and for green digits it is
             DMS-20-PC-1-DCM-G-C.    The LED's are 0.37" high.  Do NOT purchase the 0.01 volt
             resolution type (has an extra digit), as it is WAY overkill, and the always changing
             indication on the right-most digit will drive you crazy.  You need only 0.1 volt resolution,
             even for critical work on your bike; and the only such work is in setting the voltage
             regulator for the alternator; or using the meter with leads attached as a test instrument
             for setting the Voltage Regulator or measuring circuit drops.  Some manufacturers will
             call this type of meter I recommend a 3-1/2 digit type.  That basically means that at 10
             volts and higher, it simply adds a digit 1.   Heed my NOT get the 0.01 volt
             resolution meters.
      There are cheap "equivalents" to the Datel unit, sold on Ebay.  They SEEM to be OK.

Back around 1999 or so, I designed a special 2-1/16" round faced digital voltmeter, and had a company run off a batch of them.  The Company was originally called Intellitronix (C.R. Industries) and became Nordskog, in the USA.    May still be at   I sold all of them to Airhead owners except that one production version was put on my own bike, and I put my personal prototype on another of my Airheads. A few years later, I wanted a much larger batch made, and the company refused. I could not find another company to make them inexpensively, so dropped the project.  Later, I found nearly an identical meter was being sold by them to various hot-rod shops, such as Summit Racing, who resold them to the public. Guess who developed them?
  These plastic-cased meters are actually pretty darn good.  Various types are available, some with push-buttons on the face to enable storing peak voltages, ETC.

I HIGHLY suggest that the electrical connections be cleaned, particularly at the two fuses in the headlight shell. Be sure the starter motor solenoid connections are TIGHT. Be sure the starter RELAY has no corrosion at its spades...even unplugging and re-plugging in that relay can help, often a lot.
That relay is a KNOWN BAD PLACE. You can modify the wiring there, by JOINING ALL RED WIRES externally at the female plug. You MUST do it neatly. When corrosion gets bad enough at that relay, the entire electrical system will shut down, COMPLETELY.

Some later dash voltmeters can be calibrated to match actual voltage at the battery (which is typically a wee bit higher), or, to just calibrate the voltmeter for wherever you might reconnect it to....or, just for the stock wiring.   Remove the LAMP and use a flashlight and look down the hole.   If there is a small slotted place, that is the adjustment.    If the stock meter damping fails, the meters can go crazy.  Usually happens with the turn signals on.  That can also happen from poor connection joints.

NOTE that BMW bike voltmeters are dampened against some types of vibration, and CAR voltmeters will swing much more wildly, so a CAR type from a junkyard may not be a good choice.


25.  If you have a 1979-1980 R65 (maybe R45 too??), check the front ignition coil mounting bracket.  They tend to crack, and the ground wire there becomes disconnected.   You will find funny electrical problems if that happens (like maybe a crazy tachometer, lights doing weird things....).

26.  empty on purpose

27.  A RARE, but super-annoying problem, because you likely will go CRAZY before you find the answer, is one of the 1981+ electronic ignition airheads, that typically will idle OK, but won't raise its rpm up properly.    This problem acts somewhat similarly to a hole in the carburetor diaphragms.   The actual problem is a poor ignition kill switch at the bars.   Cleaning that switch may not fix the problem.  Bypassing the switch will show whether or not the problem is that switch or not.

28.  Blown fuses, different types, and various things to know:    Once in awhile I get faced with a blown fuse problem...or someone has this problem and contacts me.  Sometimes the fuse has been irregularly blowing, and is used to protect more than one item (fuses on BMW airheads and most fuses on Classic-K bikes ARE like that).   Once in awhile someone has installed a glass fuse with pointy metal tips, that is the American style of replacement fuses for the 8 ampere German-style which is an open type on a tiny piece of ceramic, often reddish or white in color...with the fuse element also being the formed-tip.  The American style (whether or not actually made in America) uses a metal cap bonded to the glass tube, and the internal fuse element is bonded to the caps.  That type is NOT as reliable as the German type, and the American type has been known to 'open', withOUT it looking 'blown'.  This is easy to check on your ohmmeter if the fuse is removed....or, I simply use a voltmeter across the fuse, or at one terminal, then the other...or, a test light across the fuse.  When a fuse is blowing relatively often, or perhaps even immediately upon the ignition being turned on or power otherwise applied, it is sometimes a Pain In The Ass to determine WHAT is wrong.  Is it a shorted wire...from frayed insulation or a pinched wire perhaps?  A shorted horn or horn that needs internal service?  Bad wiring at a tail lamp? is an old technician's TRICK, that can usually speed up the process when an initial look-see makes you think things will be difficult.   I keep an old headlight lamp on hand, with a cheap headlight socket attached (from NAPA, etc.) and at the ends of the wires I put smallish insulated alligator clips. Most of the time only ONE section of a hi/lo headlamp has blown, so use the section that has not blown.    Remove the fuse that has been blowing, and substitute the headlamp wires.  A stock headlamp bulb of 55/60 watts will only pass ~5 amperes, even into a direct short circuit.  Connect the lamp, and if it glows brightly, start tracing down the various wires and devices connected to that fuse holder.   When you find the problem, the lamp goes OUT, or greatly dims.

29.  Ignition points for 1970-1979 Airheads:   BMW has been shipping wrongly made points sets, made in China.  The rubbing block is too long, and you cannot get proper timing, etc.   I suggest the Noris points from such as Beemershop, etc.

30.   High idle after warmup? There are several TESTS for proving that the ATU is at fault (and not, say, a vacuum leak at the intake rubber hoses, no free play in the throttle cables; or a mal-adjusted idle mixture screw).   In some instances, just turning off the engine and restarting it after it was already hot and exhibiting the very high idle, is enough to reset a stuck ATU, so try that.  If that now shows a normal idle, it is likely a ATU problem.   If not get a friend's help.  First take the bike for a ride, and if the idle rpm went quite high after a FULL WARMUP of the ENGINE CASE, then pull the bike up to a nice big object, like a brick building.  You could also just use the front brake.  With the bike in gear, let out the clutch very slowly, loading the engine and allowing the engine to slow down to about normal idle, perhaps 900-1100 rpm.   Have a friend use a timing light, triggered from the left spark plug, point the light at the timing hole. If the timing is well-advanced, then the ATU IS THE PROBLEM.  Prove it by pulling in the have a high idle rpm again, right?

31.  Information on changing to euro switch gear....and in general, replacing /6 switch gear, with the 'problem' of extra wires, etc....see article 38B.  I will eventually put step by step information there, to cover all models.

32. Once in awhile I hear of someone who has a bike that is in known good state of tune...valves and timing set correctly, good spark plugs, good coil(s), carburetors carefully checked and are good.....ETC....but the bike is difficult to start, AND RUNS ON ONLY ONE CYLINDER FOR AWHILE.
This may be the ignition module.   I describe this problem in my article, but you can also find a version of it in Oak's column of November 2011 AIRMAIL.

33.  Sometimes someone wants to modify a bike's wiring so that the engine will run in PARK or HEADLIGHT position.   This allows the headlight to be turned off in one position.  In the early stock airheads where this is possible, the 30 terminal of the ignition switch is red, for + battery power. Terminal 56 has a white-yellow wire for the headlight.  Terminal 58 has a gray wire for the parking lights function, and terminal 15 has a green wire for the ignition.   MOVE the green wire to terminal 58.
DO NOTE THE FOLLOWING:  Many German motorcycles have a PARKING position of the ignition switch, in which the key can be removed in that position.  It is possible that almost any key that can be pushed into the lock, will turn the switch to PARK position.

34.  Versatile relays that can work fine for most functions in your motorcycle, such as switching lamps, running horns, starting, etc., is the Bosch (now Tyco) 330-073, rated at 30/40 amperes and 12 volts, SPDT, 5 pin, with tab for screw (tab area can be removed); or the Blazer DF005 or DF005W which also has a tab/screw mounting.

When a battery is getting old OR getting closer to failure (even not very old batteries can start dying), if your stock BMW dash voltmeter is wildly swinging during use of the directional's flasher, and you have already checked the wiring and connections at various places, the battery may need replacing

06/29/2003:  Total revision of entire article, combine electrical hints & electrical problems pages, moving
                    some items to appropriate places on the website.
07/20/2003:  add #20
09/05/2003:  add information to #2; modify #3,  #7, #13 and #19 all slightly
09/21/2003:  add note 2 to item #8; move #18 information to #8, add new #18 information, modify #19.
01/05/2003:  add #21
03/15/2004:  Corrections to item #6...several actually.
04/11/2004:  Expand #3 with all the red information
07/05/2004:  Expand #8
10/15/2004:  Redo and greatly expand #15 for maximum clarity
03/21/2005:  expand on neutral switches
03/28/2005:  update #3 for hyperlink for cricket fix; revise #4 slightly
04/09/2005:  add hyperlink on 21
11/27/2005:  In entire article, go through and clarify things.  Add R100R information too.
11/23/2006:  Clarify Monolever 1987+ diode information inside starter relay
04/15/2007:  expand #4
01/06/2008:  fix chicago club's hyperlink and description
01/07/2008:  fix vetter's URL and url
06/28/2008:  minor clarification about monolever diode problems
10/28/2008:  Add #23
02/23/2009:  Clarify #13
06/08/2009:  Expand #23.
11/04/2009:  Add #25.
11/21/2009:  Move #26 information from end of #3 and make it #26.  Go over entire article for clarity.
12/05/2009:  Add Signal Stat information to #23
02/11/2010:  Add information to #27
03/15/2010:  Expand a bit at #22.
06/20/2010:  Expand a bit at #23.
11/20/2010:  Add #28, previously in another area of the website
02/16/2011:  Add #29
03/29/2011:  Expand upon #6
05/09/2011:  Expand #10
06/07/2011:  Add #30
08/29/2011:  Add #31
09/09/2011:  Edited #24
03/24/2012:  Add 33
07/04/2012:  Expand 4B and a bit of cleanup (tons more needed!!)
08/01/2012:  Clarify #23
08/13/2012:  remove link to relay article; it no longer is there
09/27/2012:  Add QR code; add language button; update Google code; clean up article a bit, but no
                    technical information changes (the language button was removed in 2013)
03/30/2013:  Add some to 4B about the diode.
08/03/2013:  Revise 6 entirely, for clarity, WITH added information.  Prompted by an article I posted to the
                    Airheads LIST.     Also revise 3, 4 and 5, strictly for clarity.
02/17/2014   Revise #33; minor other changes.
02/23/2014:  Revise 4B extensively, and slightly in 4D.
04/27/2014:  Add 35.
07/31/2014:  Add note on wrongly interchanging the horn and starter relays, and add note on use of
05/19/2015:  Incorporate much more information on voltmeters and clocks
01/18/2016:  clarify details on the diode involved in the neutral switch and clutch switch circuitry.

in process:  review entire article.  Justify left, change h. lines, metacodes update, increase font size, change to all Times New Roman;....ETC.
Expected completion date:  February 20, 2016


© Copyright, 2014, R. Fleischer

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