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BMW Airhead Motorcycles:

The Slash 5 (/5) starter relay 'cricket' noise & starter problem,
R50/5, R60/5, R75/5.

Copyright, 2013, R. Fleischer
article 37

ALL /5 bikes should have this starter relay modification performed if the original style of starter relay is being used!

As far as I know, BMW NEVER FIXED THIS PROBLEM!  If you should purchase a new starter relay from BMW for a /5, and happen to open it up, do let me know if it was factory modified, and take closeup photos, numbers and internals.....

'Cricket' was a term put forward by "OAK" Okleshen.  He did more than one article for BMW MOA News (now BMW-ON) on this problem.   One reference to a fairly complete version will be found in the March 1977 issue of BMW News (further information in October 1977) (and a reprinted article April 1978), and an edited major excerpt will be found in the Chitech BMW Electric School Manual in Appendix F.  That is THE best BMW Airhead electrics manual ever published, and still available, see or

NOTE:  The below article includes a fair amount of additional information from me that was never put in the above articles.

The /5 starter relay problem:

NO OTHER BMW AIRHEAD, JUST THE /5, had this transistor circuit in the starter relay.   Only in the /5 was the 'starter protection feature' incorporated this way, into the starter relay.  You might see references to this /5 relay being the "Starter Lockout Relay".  They are one and the same relay in the /5, no matter the name.   I look at this special relay as a combined 'Start' &  'Anti-Start' relay, because its additional purpose is to prevent energizing the starter motor AFTER the engine is running.  It is too bad that BMW did not fix the relay problem ....or, use the circuit/relay in later models!

Function #1: Operates just like all the later Airhead starter relays, for sending electric power to the starter motor solenoid (the solenoid is a VERY heavy duty switch/relay in itself ...THAT function is in ALL BMW Airheads).

Function #2:  The additional function in the /5 (only) starter relay is done by the very simple transistor circuit inside the starter relay metal can.  If working properly, the circuit prevents you from being able to run the starter motor after the engine is running. You really do NOT want to engage the starter motor when the engine is running. It is hard on the starter motor and very hard on the 'gears' function of starter motor and flywheel outer ring gear teeth.  The no-starting after engine running function may not work well at quite low idle rpm is variable.  How the protection is accomplished will be described later in this article.

After the /5, a clutch switch and neutral switch are interconnected to perform a purpose that is not up to the same level as the /5 protection level in regards to a running engine, but certainly is OK.

The /5 had no clutch switch at the handlebars. The /5 also did not have a neutral switch with the same functions as on the 5 speed transmission models. In the /5 the neutral switch simply operated the Neutral lamp.

***The /5 can have another problem, a rare problem of 'no start' ...the starter relay does not work at all, yet all of the starter circuit seems to test OK.  The problem can be an open alternator voltage regulator, or an open rotor.  THAT can be confusing to you!  It is not being discussed further in this article won't get any or proper charging if either of those parts failures happen. ***

It is best to modify the /5 starter relay unit and thus retain the safety features.  The modification described will ensure that it operates under cold and/or marginal battery situations.   You can do this yourself, or print the instructions & take it ...or; the URL address to this page ... to your friendly electronics shop.   The fix is simple, it works, it fixes potential problems in cold weather and slightly or more weak battery.


The problem usually shows itself when you have either a slightly low battery, OR cold weather, OR BOTH.   In either or both of those conditions the battery voltage will be just a small amount lower than if warmish and fully charged.     When the starter button is depressed, the battery will, no matter what condition, have a lower voltage due to the electrical drain.   The 'starter relay' will not stay fully pulled-in, so it will not have reliable contacts closure and thereby won't send electricity to the starter motor solenoid continually and/or consistently.  The starter solenoid on the starter motor likely make a loud and ratchety noise ...or a fast clicking or clackety-clack noise, ...which was called by us old-timers 'The Cricket' (although sometimes a different noise is heard, meaning the starter relay is 'ratcheting' and the starter solenoid never pulls-in to make its loud noise).   For either situation, the starter usually does not rotate.  

The first thing anyone typically suspects is a bad battery, as this sort of chattering noise & failure of the starter to rotate the engine is common on all sorts of vehicles, including automobiles, when the battery is quite poor, or heavily discharged.   SOME, maybe many, /5 with the original UNmodified relay will seem or actually be OK, and maybe you will never experience the problem! is a matter of small differences in the starter relay transistor, and internal adjustment.  I still strongly recommend the modification, as you MIGHT have some combination situation some day and have the problem, even after years of no problem.

The relay in question is a metal can, under the fuel tank, on the left side, farthest forward.

The entire cause is two-fold:  (1) low amplification (low gain) of the transistor circuit inside the /5 starter relay; and, (2) the circuit was not properly temperature-compensated.

The circuit was affected by battery voltage, which lowers with cold and with inadequate charging, and with loading, of course.  Since energizing (or trying to energize) the starter motor will drop the battery voltage even more due to the current flow, the problems feed each other. Things can be even worse if connections to the battery are corroded or otherwise poor, you have loose connections someplace else, or a poor battery.

Replacing with a generic relay or modifying to remove the transistor function on the original type of relay:

It is best to modify the original /5 starter relay as described in this article.   Once in awhile, that relay is such a mess that someone will replace it; or, just wants to, even though it is easily repairable (such as to burnish the contacts, or do the Modification).  Good reasons to replace the relay could include water damage, or an open coil.   The original type of relay is pricey, if you can find a new one. It was still available the last time I checked, November 2016, but $150 or bit more!   You could probably find one from a salvage /5, and modify that relay.  SOME will choose to simply remove the bad relay and substitute a generic relay.

Almost any 12 volt coil relay with at least single pole single throw contacts (SPST) will work just fine, and the Bosch (now Tyco) black plastic-cased ones are cheap and work fine, most auto-parts stores have them.  You can use a SPST, DPST, or a DPDT, etc.   You just need to know how to mount and wire that relay.   If you substitute such a simple relay, IT WILL NOT have the /5 transistor circuit, so it is then possible to engage the starter if the engine is running and you push the starter button, which you should never do.  That is the same situation as later Airheads, but they have a 'sort of' protection.  That is, the starter will not be able to be turned on unless the clutch lever is pulled backwards or the gearbox is in neutral.  Cars won't engage the starter, even if you tried, unless the gearbox is in N or PARK.  It varies for cars with manual transmissions (you may have to press the clutch first). 

Again, never engage the starter with engine already running. On the /5 you do NOT have the neutral switch nor clutch switch 'protections'.   So, yes, it would have been nice if BMW had incorporated the properly operating and designed /5 relay into the later models, but BMW did not, due to other considerations, including the VR or ROTOR failure noted earlier.

I recommend using the stock /5 relay, but with the modifications shown later in this article you are reading.  Certainly, use of a generic relay will work ...just do not press the starter button unless actually trying to start the bike.

It is possible to modify the original /5 relay to eliminate the transistor circuit, but I do not recommend that.  That would be done by disconnecting the blue D+ wires, and running the D+ terminal of that relay to ground.    

Nerdy electronics guys will perhaps figure out that you can modify a conventional relay and the starter relay circuit, to get the protection effect of the transistor can relay in the /5 ...I do not suggest this unless you understand the circuitry pretty well and have considerably more than average electrical ability.

If you plan to install a GENERIC relay and thereby eliminate the safety function, simply disconnect the blue wires from the original /5 relay at the D+ terminal of that relay. Join those wires, and insulate them.  Join the red wires that went to the original terminal #30 of the /5 relay, and connect them to one contact of the new relay. Connect the original black wire that went to terminal #87 of the /5 relay, to the other contact of the new relay. Now, the only connections left to install are to the new generic relay's coil.   One coil terminal must connect to the original brown-black wire that was on the original /5 relay terminal #31.  How you now connect the remaining new relay coil terminal is up to you.  There are TWO methods to keep in mind:

1.  If you connect the remaining relay coil terminal to a source of battery power that is always ON, then ANYtime you press the start button, key turned on or not, the engine will be rotated.   This is a bad idea, but I have seen folks do it.

2.  The original wiring had terminal #15 supplied with power AFTER the key switch was turned on.  That is the connection to use.  The associated wire color is green-black.

How the original transistor circuit, located inside the starter relay, operates in the /5:

The output from some of the small diodes on the diode board (that supply the sensing voltage to both the voltage regulator and the GEN lamp) are connected to the /5 starter relay at terminal D+.    Inside the starter relay can, a one-transistor circuit sends electricity to the relay coil.  The relay, when energized by you pressing the START button, causes the relay contacts to close, which sends electricity to the starter motor solenoid switch.    The transistor circuit is so arranged that once output from these small diodes is present (alternator is rotating, near the charging mode or higher), the transistor does not allow the starter relay to operate its contacts.    A tiny control, an adjustable resistor, called a potentiometer, some may call it a rheostat, is inside the relay housing, and was factory adjusted for proper operating performance.  No, you cannot necessarily get reliable operation from trying to adjust it.


The transistor is a PNP silicon type, probably a type BC213B or similar, with the emitter connected to relay pin 15, thence going to the ignition switch (and GEN lamp).  NOT modified,  the Base of the transistor goes to the potentiometer wiper, one end of potentiometer to the transistor emitter, other end of the potentiometer goes to pin D+, which goes to the small diodes and voltage regulator and lamp. 

The voltage regulator is slightly turned on when the key is on, and that allows this point D+ to appear fairly low in resistance, via the rotor which loads the regulator.   (keep in mind the RARE problem of open rotor or regulator, mentioned well above). The collector of the transistor goes to the relay coil, and the other side of that coil, terminal 31b, goes to the starter button.  During key-on, engine not running, the transistor is supposed to be turned on, via the regulator-rotor circuit, ALLOWING the relay coil to be energized when the starter button is depressed.  In cold weather, perhaps combined with a slightly lower battery voltage initially ...and especially during attempts at cranking ...the transistor MIGHT NOT 'saturate', meaning it would not turn on fully. Restating this slightly differently cold weather the gain of a simple uncompensated transistor circuit goes DOWN.  At the same time the battery might actually be a wee bit down, & the voltage would be a wee bit lower, making things even worse for that transistor, which is powered by the battery.   In actuality the circuit operation is a slight bit more complicated in how the transistor is operated, but that is good enough for this discussion. 

The schematic for the UNmodified relay circuit is identical to the below sketch, with the following exceptions:
1. The diode and 470 ohm resistor are not used.
2.  In place of both, is a potentiometer, with the wiper connected to the base of the transistor and one pot end connects to terminal 15, the other to D+.

NOTE:  The GEN lamp is wired to 15 and D+ and not shown here, as the lamp is EXternal to the relay box.

A schematic diagram of the MODIFIED relay circuit, and description of parts and functions, AS MODIFIED BY THE PROCEDURE:


Part 1:  General description:

You will be removing the relay from the /5, opening it up (de-crimping), and making relatively simple modifications.

Be SURE to disconnect the battery (disconnecting ALL leads at the negative terminal is recommended) before touching or removing the relay.   DO NOT do this job yourself if you are the ham-fisted type!  NOTE where the wires go when removing the relay, your bike could have been modified, or have an anomaly. Compare the wire colors and terminal numbers:

Terminal 87:  black wire.
Terminal 15:  green wire, green/black.
Terminal 30:  THREE red wires.  There are TWO terminals marked 30, or joined as #30.
Terminal 31b:  brown/black wire.
Terminal D+:  TWO blue wires.
The relay bottom has the connectors numbered, you can make notes or a sketch.

NOTE!.... The innards can be wrongly installed 180 around in the metal case.  Therefore, before un-crimping and removing the innards, be SURE to MARK the relay can AND the relay base, so they can be re-installed the correct way ...thus the wires on the bike will fit properly when reinstalling the relay onto the bike backbone.  I put a scratch or pencil or marker pen mark on the can, and the base, next to each other.

Part 2:  How-to:

You will be removing the small adjustable resistor (potentiometer) entirely and adding two inexpensive parts. For access to the inside of the relay, you must UNcrimp the cover. As noted above, mark the case and relay base, so innards are not reversed when reinstalling into the case.   UNcrimp NEATLY, and re-crimp it back in place when you are done ...NEATLY ...and with the innards in the correction position.

Parts:  You may well be able to have the local TV shop give you these parts from their "junk box". NOTHING critical about them at all.

a.  ONE only commonly available 470 ohm 1/2 watt (or 1/3 watt) resistor will be installed & connected to terminal D+ inside the relay can on the circuit board, & the other end of that resistor to the transistor BASE terminal (BASE describes an electrical function, not a physical location, although it IS often printed as B on the bottom of the part.  A simple transistor usually has three leads, called base, emitter, collector).    These resistors usually come with bands of colors on them, the bands signifying the value in ohms.  For most common 470 ohm resistors, the first band, always the one closest to one end, is yellow (4); the second band is violet (7); & the third band is brown (signifying zeroes, in this case brown means ONE zero).  There may be another band, typically it is silver or gold, signifying percentage tolerance ...disregard that, it is of no importance here.   Radio Shack probably still sells 5 of these in a package for ~ a dollar, part 271-1115 for the 1/2 watt.  When bending the resistor leads try not to bend too close to the resistor body, which might strain the part.   Some types of resistors are coded slightly differently, with one or two extra bands of color be sure you get a 470 ohm resistor.

b.  ONE common silicon diode, any type (generally, so long as it is NOT called a Schotky & NOT called a ZENER), & it may be rated from ~1 ampere to as much as 2-1/2 amperes (anything larger is hard to fit).  The diode may have any voltage rating available.  It is to be connected, circuit-wise, from the BASE of the transistor to the EMITTER of the transistor. You MUST connect the diode so the END of the diode that has the LINE (painted band) on it connects to the EMITTER.  Radio Shack probably sells packages of 2 of these common diodes under part number 276-1101 (up to -1104) ...any of those are OK.   Packages of two are probably ~~ a dollar.   Wherever you obtain the diode, the diode might have an arrow and line printed on it, or just the line.  The line signifies the end wire that connects internally to the cathode of the diode (arrow, if present, is anode), and it is the LINE end you will be concerned with.

This is all done at/on the original circuit board potentiometer mounting and connecting holes, and NOT at the transistor part leads.

Warning!!!  Be very careful in removing the potentiometer.  It will NOT be reused, but you do not want to damage the coil wires.   It is best to first use a product called Solder Wick, or similar solder-sucking braid, and you should add some extra soldering rosin, to soak up all the solder around the three potentiometer leg leads.  THEN, with the soldering iron (cleaned tip) back on those leg leads (one by one), bend the potentiometer lead vertical with a small sharp knife blade.  Then snip the lead flush with the board on the soldering side, which shortens the lead for ease of removal from the other side, and then GENTLY remove it, probably with narrow long-nose pliers or forceps, from the other side of the board, using the soldering iron as needed.  Be VERY careful not to nick or break the COIL wires!!

Below is a photo of what is inside the can.

Below is a close-up view, of an UNmodified relay. Note the adjustment slot in the potentiometer.

Below is a top view of the stock, UNmodified /5 starter relay, with the potentiometer (POT) in the lower center area, and the black cylindrical transistor on the right.

Below is a picture of a modified /5 starter relay, & to the right in the picture is a new potentiometer, similar to the one you will be removing, but NOT replacing.  The resistor is in the center upper area, and it has colored stripes.  You can see the yellow stripe, then purple stripe, then brown strip, then silver stripe.  The colors identify the resistor.  Yellow means 4, purple means 7, brown means 'one zero', and the silver is a tolerance, unimportant here (gold color also OK).   Thus, from the colors, the value of the resistor is 470 ohms.  Most modern resistors have extra color bands.  Check the resistor with your ohmmeter, and be sure it really is ~470 ohms, and learn how to use your ohmmeter.  The diode, which in this poor photo appears to be a black cylinder directly below the resistor, has a silvery line on its left end, which is hard to see here.  The resistor RIGHT wire and the diode RIGHT wire (anode) connect to the same soldering point.  The line end of the diode, called the cathode (the flash reflection makes it hard to see), is to the left side. The resistor in this photo is an old-fashioned type called a 'carbon composition resistor', but modern types, see 2nd picture below, are fine.

BELOW is another view, this is a different relay, the resistor here is a more modern type.  Some resistors have one more color band. It is easy to see the diode silver (or gray) line here.  It makes no difference which direction the resistor is mounted.  For the diode, it MUST have the gray or silver band downwards to the left, as shown.

Before you re-assemble the innards into the can (correct direction >>>...line-up those case and base marks you originally made! and re-crimp), you should clean & burnish the relay contacts.  Use a very fine grit sandpaper, 360 grit or higher.  This is to be done very lightly!   Burnish both contacts.  Do NOT use emery paper, and do NOT force anything into the gap, you do not want to change the gap distance.  

To do it, pull the sandpaper at 90 degrees, that is, parallel to the points NOT 'round' the points, they must remain shaped as before.   Use your fingertip to put a SLIGHT amount of pressure on the contacts while using the sandpaper (or burnishing tool). Just a tiny bit of sandpaper is needed,  and do ONE pull-through, then insert the sandpaper again and use it upside down, ONE pull-through.

THEN slide a piece of clean white NOT SHINY paper through the contacts (hold again with very slight pressure with a fingertip), to clean off any sandpaper grit.   I put ONE drop of a solvent such as alcohol or acetone or MEK, on the paper first.

As has been noted previously, be sure to line up your previously made marks so as to put the innards back in correct position in the metal can.

Install the innards, and try to NEATLY as you can, fold over the de-crimping you did previously.  Seal the crimped areas using something like RTV, but do NOT use the type of RTV that has a smelly acetic-acid (vinegary) component!   I use only a small amount of sealant, on the edge of the terminal board, as I insert the last bit of the innards ...and then a tiny bit more all around after the contents are inside and the re-crimping done. The sealant will prevent or greatly reduce contacts problems from atmospheric effects in the future.

TESTING:  The relay can be bench tested using a 12 volt supply and a lamp, but you can just install the relay and see if the bike starts OK.  The formal bench-test method I had in a short section here was confusing to folks, so I removed it.  If you want to test the relay for anti-start, after the alternator is spinning you can unplug the thin black wire female connector at the starter solenoid, and use a test lamp on that wire, to ground.  Pressing the start button, engine running at reasonable idle RPM (1000?), should NOT light up the test lamp; but the test lamp should light up, key in, ignition on, engine not started.

First posted to Airheads LIST about 8 pm on 07/24/2003.  Then edited & put here about 9 pm & edited for references.
07/27/2003:  Final editing and release.
09/30/2003:  Slight clarifications and references.
02/04/2004:  Update in preparation for pictures.
02/05/2004:  Pictures and text, article completed.
02/06/2004:  Final edit and release.
03/23/2004:  Edit for clarity.  NO important changes.
11/20/2004:  Revise extensively to eliminate problems in understanding the procedure IF using a generic relay & not the original type of relay (whether modified or not).  Add information to make it just about impossible to misinterpret the modifications, no matter if /5 relay or generic relay.
02/25/2005:  Minor cleanups and reduce contrast on one photo.
09/10/2009:  Clean up article...typos, grammar, colors; fix unclear information;...general housekeeping. 
11/25/2009:  Add two more views.  Clean up article a bit for clarity.
10/07/2010:  Clean up article a bit for what I hope is now 100% clarity.
06/01/2011:  Add diagram at end of article, for the Nerdy.
10/14/2012:  Add QR code, add language button, update Google Ad-Sense code, slight editing and re-arranging in the article.
2013:           Remove language button as the Javascript caused very slow running and some hangups on some browsers.
09/17/2014:  Clean up article a small amount; remove testing information, as it confused people.
12/14/2014:  Add simple wiring color coding note.
05/25/2015:  Revise for simplicity, Add notes & red lines to photos to identify parts better.
03/30/2016:  Update meta-codes, improve article fonts, colors, layouts, & a bit more on clarifications.
11/19/2016:  Update entire article.  Fix metas, fix scripts, fix old style HTML.  Move circuit sketch upwards (previously at end of article), and add full explanation of pre and after modifications, and how things work. 

Copyright, 2013, R. Fleischer

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Last check/edit: Wednesday, January 17, 2018