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Adding Running Lamp Function To Turn Signals

Copyright, 2017, R. Fleischer
34; O15

This article deals specifically with converting Airhead rear turn signals into running lamps, while retaining the original turn signal function. Considerable information is applicable to the front.

This article does not deal directly nor specifically with conversions to the Classic K-bikes, such as the K1, K75, K100, K1100, but much of what is in this article on the physical modifications is applicable to K bikes, Oilheads, etc.   The K-bikes have a bulb-monitoring relay; which complicates matters, & information on modifying them is in item #2 in

This conversion may add to safety.   You get more rear facing lights, & you will have two lights that are illuminated in case your one stock 'running' lamp burns out.  Many bikes have only one rear running light ...if it fails are invisible to cars coming up to your rear; which is one of the arguments for this conversion. My primary argument against this conversion is that the turn function is, or can be, less noticeable to car drivers ....due to the running lamp function in the same lamp, same housing.   You must decide for yourself.   Proper installation with proper color of lens & proper lamp bulb may negate such an argument.

The conversion may or may not be legal in some States, not sure anymore ....if the lens is not re-colored to be red (or the lamp colored red).  Some may not care if lens or light color is red or amber.  Careful selection of bulb & possibly inclusion of reflective aluminum foil may improve brightness; but this is a minor point.  There is a potential problem with the basic method which I do to convert the rear turn signals into running lamps (I sometimes do the fronts too, another story).   If not done well, the turn signals are not hugely distinctly different from the running lamp function. Properly done they certainly can be very distinctly different. Several ways to go about it, including a small unpainted or no red insert area, in the middle of the lens, or, a band across the center.  One can find red bulbs plus use aluminum foil as a reflector, if needed.   The reflectors & lenses of the stock bike are optimized for incandescent lamps, not LED types.  I do not recommend LED lamps, of any type I have so far seen, for purposes of this article; wide angle LED lamp structures may be available.

Red lenses have been available at times, a near perfect direct replacement for your amber ones; you need only to provide a rubber gasket (easy and only if you wish to), and in a few instances about a minute of filing, depending on if plastic or metal case.  The ones I have seen have an even better than stock amber lens light diffusion/reflection in the lens.    Check such as Ebay.  The ones I saw have number K22750 and K32724 on the plastic cover & were made by CoolBeam MTP; they are marked as SAE & DOT approved.  These are hard to find in the USA.  I have a set on my own motorcycle. If you find a source, PLEASE let me know so I can publish it here.

The conversions in this article are for incandescent lamps.  You are free to experiment with plug-in LED lamps,  I have done only somewhat limited experiments.

California, as well as other States, have very specific requirements about lighting.  The requirements are not the same for all States.  You may want to find out what your State vehicle code says on the subject.  You can use such as Google, to search for the vehicle codes.  I won't get into the legalities, that may vary state to state, but this conversion is believed legal, or at least quasi-legal, if done correctly, everyplace, because of Federal law.

California V.C. 24603 says, amongst many things, that California does permit, for a vehicle manufactured before 1/1/79, to have red or yellow stop lamps.  A section in 24603 says that supplemental stop lamps on the sides, can flash towards the direction a turn is being made.  Some States, if not most or all, will have such or other allowances, ordinances & regulations.     This can mean that you can add red color to the lens or lamp, or partially, or leave the turn signal lenses amber, etc.   Think about it!

This type of conversion can be done to add running lamps, or to add braking lamps, or both.  I've experimented with adding those plus turn indicating lamps. I've converted just about all of my motorcycles to have multiple run and brake lamps.

The Federal Government also has its code sections, not difficult to find, probably more difficult to wade through.

The bottom line is that if done correctly, the two filaments in one bulb (in some cases two bulbs) in the same housing, can be made to look very distinctly different; and probably are legal. I've personally never had any problem with Authorities for any of my conversions.

MORE and DETAILED considerations ....and notes:

For the rear turn signals, in the past I have left the lenses stock, that is, amber.  For my own 1995 R100RT I found red lenses on Ebay!  I have also used red lens material on some of the first 'new style' conversions I did, so that following vehicles see red, but to the side is still the amber color of the original plastic covers. If the hot bulb does not touch the red plastic material, I found that almost any common red plastic material that will pass light, perhaps 1/16"  or less thick, will do well. Hobby stores often have small bits & pieces of colored plastic sheeting. As noted, I also did a lot of these conversions without adding red material. A few I even painted inside the lens.  Some I masked & painted such as to leave an amber stripe horizontally, centered vertically, and about 1/4" in height.   I have also done some with a masked amber round area in the center. You could consider using a red lacquer or other plastic compatible coating on the inside of the amber plastic lens....but only on the extreme rear, not the sides of the plastic lens (maybe not noted).  Consider also just leaving the lenses alone, and not using colored inserts, not painting, not using colored bulbs.  I had good luck with red nail polish on the inside of the otherwise stock amber plastic cover.

In one conversion, I left the original amber plastic lens alone ...but installed a red lamp ...I found these lamps commercially available.....and I then used a sharp knife to remove a fair amount of the red material from the lamp that was forward (as fitted) from the rear top of the lamp.  That gave white light to the sides, red to the rear.   It worked OK, but there was no super easy way of replacing a lamp, red lamps were then not common.  They are more common now ....perhaps as 1157R or 2157R.

NOTE #1: Much of this article's information is also applicable to the front turn signals.  If you do the turn-signal conversions, be SURE that the turn signal function is very distinctly different from the run function.

NOTE #2: The turn signals on the stalks models are very similar, front & rear. The turn signals in the RS & RT fairings are different, but the sockets similar. Thus, one may use much of this article's information to convert the front turn signals.  BUT... for the front turn signals, while they can be converted in a similar way, I have also used a method in which I drilled the reflector & installed a small lamp in a separate small socket, sideways. That was an experiment. I somewhat prefer the conversion of the socket as described below.  Obviously, for the front's, you do not use red material or red paint.   The front socket setup is different for the faired versus un-faired models.  But, the principle is exactly the same.  You may have to run a wire to them ...on the RT, perhaps from the eyebrow light  ........simple!

NOTE #3: I did contemplate making the rear turn signal housings 'all function' ...that is, incorporating a few diodes to make them act as run & turn; and using the diodes to add a brake light function!!  I never did the engineering work, although it most likely can be easily done.

General installation notes:

Remove the outer plastic lens cover over your taillight and the lens covers over the turn signals, pull the innards out just a bit, & look at things.    Read this procedure through, as you look at these areas.

Plastic lens covers should not have their mounting screws over-tightened will break or crack the lens.  Some plastic lens covers can ...or should ...only be installed in one direction.  A moisture drain area is usually provided on the lower edge.  Some can not be installed with the top marked area on top!    ....that is normal!

The #1176 lamp does not have offset pins.  I do not recommend you use that lamp or the different part numbered non-offset socket it requires. In my very first conversion, decades ago, I originally used that 1176 lamp, using a mickey-mouse jumper soldered to a lamp contact.  Why? ...well, I had lamps & sockets.

On a later conversion I modified a BMW single contact socket to two contacts. Not recommended (mickey-mouse), & because you would have to identify the bulb contacts as hi & low power, each time you changed a lamp, meaning some soldering for every bulb change unless you hand-made the contacts ...this is all very messy.  I have also seen others do this, please do not!   For those that insist on knowing about the #1176 lamp:   12.8 volts, 1.34 amperes, a lower 21 mscd; 14.0 volts, .59 amperes, 6 mscd. Please do not use an 1176 lamp ...rather, just use the lamps & methods I recommend in this article.

Use of higher powered bulbs is not recommended.

The particular socket I have selected & recommend, has the usual two side locator openings that mate with male pins on the lamps,  but the pins are offset lengthwise in bulb fitment.  Thus the lamp can only be installed in one position, not 180 the other way.   This is standard for lamps which are often used for running and stop (brakes) function. It is standard for any two functions in one lamp usage.

Using the 1157 (2157) bulb with its length-wise offset pins is a far better choice than non-offset types like the 1176. Using a common 1157 (2157)  lamp ensures that, if properly wired at the socket, you will have a bright turn signal, and considerably dimmer running lamp, which is what you want .... and ... bulb replacement is easy, as it can only go in one way.  NOTE that the Euro type of lamp, which is quite similar enough in specifications, is number 7528, it is a good lamp.  You can use 1157, 2157, or 7528.   There is a lot of semi-nerdy & nerdy information on these lamps, here:  If you really want a lot of information, read that comprehensive article, possibly it covers every type of lamp you might use at any time, any place, in your BMW motorcycle.

When this conversion was originally announced on the Airheads List, a PS34240 numbered part was used for the socket. That is a Borg Warner product number. Pep Boys & other places sell Borg Warner. However, later, when I purchased the Borg Warner part, it was part number PT11 in their catalog. It was nicer than the Napa part, which was Echlin brand #LS6538, but that will also work OK.

Some LED lamp units are on the market, such as from, that offer a unit, such as a 1157 replacement, that has LED's pointing both sideways & to the rear.  They have a bright section & a running section.  Some reflectors will accommodate these nicely, some don't show enough of a change between run & turn.  Some flasher relays on some motorcycle models will require changing to accommodate the low drain of the LED unit.  I don't like using resistors to increase the current drain to enable problem flasher relays to work.   Now-a-days the 1157 LED replacement is available in yellow as well as red and white illumination.   The yellow works fine with yellow lenses.  While you can use white, I think using the same LED color output as the lens color is best.

I still think LED's are not as good, for visibility, in this conversion, as using incandescent lamps.  If I see an LED unit that is as good or better, I am open to modifications.


What you are going to do is modify the stock socket/reflector, which is one unit, to accept a metal socket with two contacts for a 1157; 2157; or 7528 lamp.  The particular socket I have selected has the usual two side mounting pins area, but the pins are offset in the (lengthwise) bulb fitment, so the bulb can only be installed in one position, not 180 the other way.   This is standard for these lamps which are often used for running and stop (brakes) function.

You are going to modify the stock socket/reflector, reaming the existing hole or otherwise make it slightly larger but a good solid finger press fit for the socket, sand the socket, epoxy in the new socket in the correct rotation & also for the in-out alignment, & then connect existing wires. You will add one wire for each turn signal, soldering to the original BMW socket grounding tab. This is exactly how it is already done for the rear turn signal housings that are on most airheads, said housings typically are on a round metal stalk tube.

The first order of business is to look at your bike, make your decision(s), & then obtain the new lamp sockets!   You may want to try to find red lenses.  Good Luck.

Remove the BMW bulb holder (this is part of the reflector assembly) grounding contact in the turn signal unit.  Ream the plastic center hole for a fairly tight finger-push fit about 0.650 inch diameter. It will be necessary to snip off the little original plastic tab that kept the original bulb from going deeper than a certain point (a few reflectors do not have that). Do measure & hand fit your new socket to the BMW reflector. Your socket may not be exactly the same as mine was. A common hand reamer works fine here on the plastic reflector, from both sides, a small amount of material only should be removed at a time.   You could use a round file, but please keep the hole nice & round and the less taper the better.  The socket should be a medium-hard push fit before epoxy work (do not epoxy yet).

I modified the sockets I purchased. They had a 0.350 inch diameter, 1/4 inch long tube area at the rear of the socket, a sort of  'stepped-down' area. You can easily remove the contact/wire unit through the front of the purchased socket. I ground off that socket's rear tube section to just flush & then cleaned up (IMPORTANT!)  sharp edges on the center hole where the wires pass through. ....Note:   There are several types of these sockets, be sure the sockets you get have the offset length-wise pins; that is, the two opposing places the lamp pins end up at when the lamp is installed, are not directly across from each other; one is closer to the aft end than the other!

Some sockets are such that just grinding/sanding off the rear socket tube area is not quite enough.

Install the 1157, 2157 or 7528 lamp into the socket that already has the wire, insulating washer, & spring.  Pay attention to the wires as they exist the rear hole.  If any chance those wires can contact the socket metal, then ream out the rear hole & clean it up.   Do not ream so far that the spring will fall through.   You can also add a very short piece of heat-shrink tubing (too long & it is crushed upon assembly to the bike) to each wire at its socket pin, shrinking it in place added insurance that the pin can not short to the case.  Remember, this conversion may be on the motorcycle for decades ....we want no chance of short circuits!   Once you have things properly done & cleaned up, proceed.

Remove the wires, spring, & insulating washer that has the two wire holes in it, from the socket.   Clean up the outer surface of the socket with fine grit sandpaper ...for good epoxy adhesion. Temporarily install the lamp.  Install the socket/lamp to the exact correct depth & orientation of the thinner filament. Don't push too hard on the glass.  Remove the lamp after deciding on orientation.  Double check this work & be sure that you have not mixed up the left & right reflector socket assemblies when actually installed in the bike, the thin filament is horizontal and on top.  Be sure the lamp does not touch the plastic outer cover lens ...& at the same time, the wires are not crushed at the inside.  Do not epoxy yet!    If you want to double check the functions, power the lamp by connecting the socket metal to the battery or convenient grounding point on the motorcycle, and first one, then the other wire to the battery + terminal.

Now'll be soldering to it:  The original BMW brown (grounding) wire will continue to connect to the original grounding clip...which removed clip is now replaced, & soldered to the bulb holder, after first carefully bending its long bulb contacting tab the other way (180 degrees) (don't bend the wrong part).  That tab touches the socket in that sanded area, for soldering.   Be sure you do a really clean, well-soldered job here & snip off any excess of that tab length.  You won't be able to solder adequately unless the parts are very clean & finely sanded.  You should use a rosin core electrical solder & a fairly hot and fairly substantially tipped mass on the soldering iron.  Done quickly, no reflector plastic in the slightest will melt.   You can not do this part of the job until the socket is installed the correct way for depth & round direction.  You do that by making test-tries ...that is ...test installing the socket, & its rear wires loose behind, & installing it with the 1157, 2157, or 7528  lamp. The idea here is to not let the lamp touch the inside of the outer cover lens plastic material (that means your added red plastic material if you use it) & at the same time not have the socket so deep in the reflector that its rear wires get crushed. Spend a few minutes doing this right.   If your items allow, use extra clearance behind the socket for the wires...just so long as the bulb will not come too close to the inside of the still yellow colored outer lens.  You will have to put the reflector-socket-lamp assembly into the housing, & then hold the cover onto it see the distance of the lamp to the cover.   Some reflector units have a riveted contact/spade.  Drill it out carefully, & modify slightly as required.

Your lamp may have a 'top' mark on it, if so, follow that as far as rotation of the lamp socket is concerned.  When the area marked top is on top, you should see the thinner filament is on top, horizontally.  Bulb marked or not, that is how the socket should be installed, with the lamp properly inserted in the socket.  As noted above, you can test the lamp and socket from the battery.

The right side lens fits with the lens lettering proper (top marked) ...but the same lamp assembly part is used by BMW on the left side ...installed upside down it fits only one way to the metal housing (BMW flips the housing over for the other side). This means that if you really want to do things 100% orient the left side bulb filament & socket at 180 degrees to the right one ...ending up so that both sides are the same regarding the bulb orientation, that is, thin filament on top and horizontal. Frankly, bulb orientation is not all that important ...and, I have seen variations on this stuff. BMW has supplied these housings & outer covers in more than one way & they all look the same at quick glance.   The inner reflector unit only goes into the housing in one direction ...keep that in mind when orienting the lamp, socket, & putting the outer cover up against the housing & reflector, when checking such as bulb clearances & socket orientation.  The outer covers have been made in two basic styles, any drain hole, typically a tiny horizontal area, is at the bottom if you have that drain area.

Perhaps you will want to do one side at a time, & not take the chance of mixing things up and finding something does not fit! So...inspect your particular parts carefully!

For front or rear, check the fit carefully, setting the socket to the correct depth & orientation, before epoxying! You will find you can get at least 1/8" clearance from the bulb to the plastic ...a bit on the extra side is nice in case of bulb variations in the future.  Be sure there is enough room at rear for the wires to bend sideways without being crushed!

With the new socket to the correct depth & orientation for filament, you can now clean the surface with a clean rag & bit of evaporating solvent, maybe use a scrap of sandpaper if need be.   Epoxy the socket with JBWeld Quikset or similar quick setting epoxy, a tiny dab here & there. Do not get epoxy into any slots of the socket!  You can dab in the reflector area, as well as the rear area.  I dab a tiny bit in the reflector area, then turn the unit over, leaving the reflector open side down, & do the rear.   Very little epoxy is required over-all.    Do this neatly & don't get the epoxy where it is not wanted! Be sure the depth & orientation is correct, & also correct for the particular left or right bike housing long before you apply epoxy or do soldering!

For the rear, you can (unless using a red lens; or paint or lacquer or other coating, as described, on the rear inside portion of the plastic lens) install some thin flat red plastic material (not cellophane!) into the original yellow lens (some paints may be OK, not on sides of the lens please), & as far into the lens as possible, & you need to file or otherwise shape the size of this added piece, if you use it, so its edges can be glued into the lens. want the socket depth to be such that the plastic cover fits, red insert does not touch the bulb, yet the socket/wires do not bottom/crush at the rear of the housing.  I mostly just paint the inside rear of the lens & don't use plastic inserts; as I can be creative with the painting.     Note here that I have mentioned, much earlier in this article, various other methods I have done with the lamp and lens.  Decide which you want to do. You can also decide to not use a colored bulb, not use colored material, not paint the lens, etc.  You can also consider red bulbs, such as 2157R.

Connect the original BMW wire in the turn signal housing to the brighter filament, retest with power on, to be sure you don't mix them up. Don't leave bare strands of wire here & there. Be neat!  Shrink tubing may well do a better job at keeping the connections small, as opposed to using barrel type of crimp joiners there is limited room in the housing.

You will have to add two wires from the running lamp portion of the regular center taillight (or convenient point, depending on model of bike) to the new running lamp filaments ...this goes to the less bright filament. Run lamp section is green/black on airheads (white-black on Airheads with the single dual filament bulbs in the stock taillight, such as a R80ST), inside that taillight. Do this neatly, running the wire through the turn signal mounting tube. Remember that your wiring should be neat, it may have to hold up to vibration for decades.  The ST, & some other models, are constructed differently regarding the mounting & wiring of the stalks. Make changes as needed.   It is a nice touch, if you can, to use the same wire color code for the added wires.

If you don't know which is which wire coming from the new socket, then before installing the new sockets, insert the bulb fully & properly, hold the socket outer metal against one terminal of the battery; and, in turn, touch the socket leads, one at a time, to the other battery terminal ...and mark the brightest lead connection as "turn" and mark the dim one as "run".

Be very sure that the wires are not crushed behind the socket.  Be sure the wires are not cut by the end hole of the socket.  This is extremely important!, and the socket depth before epoxying must be checked!   Yes ...I keep mentioning this point. Remember: not too deep to protect the wiring, & not too far out to keep the bulb from touching the plastic. You will have to assemble & disassemble a few times, just to get that correct ...a few total minutes. Once you epoxy it, it is not going to be moved again!

For the more anal types:
The #1157 bulb or #2157 is, on one filament, 12.8 volts at 2.10 ampere rated (this is 26.88 watts), 32mscd light output. That higher powered filament is for turn signal (or brake) function. The other filament is 14.0 volts at .59 ampere (8.26 watts), 3 mscd. That is the 'running' filament function. This is proper, that 12.8 volt rating, because when the brakes and/or turn signals are in operation, the higher drain pulls down the system voltage a bit, due to little voltage drops here and there; and, the alternator is usually not putting out anything or not much, the engine typically being at idle most of the time the turn signal is on; and, the lamp manufacturer's tend to have the bulb a bit over-voltaged anyway ...although this does reduce its life.  Don't worry about it all, I am just mentioning it in case you notice a chart of specifications.  The original turn signal lamp had the same situation. Some lamps have nominal "12 volt system" ratings, & have another voltage rating that is the real rating.  I get into these 1157, 2157, and 7528 lamps ...and a lot more depth, here:

With the lamp having at least 1/8th inch clearance from bulb to the red lens, there have been no heat related problems on my conversions.  Much over 1/8th inch is unlikely to be had with an added red plastic material unless very thin (no problem with painted lenses) ...and still keep the wires from being crushed. There have been no problems without the red lens either ...I have done about twenty of these modifications; some with no red material added. Probably not really legal.

If you use a coating, find a red paint of some sort that will stick to the inside of the yellow plastic lens quite well; thereby no need to install a piece of reddish plastic material. This means no water-based paints. Do NOT paint the inside side-walls of the yellow plastic lens.

Regarding the more common of the grounding clip styles removed from the BMW socket:
I bend the forward facing portion that originally contacted the side of the original BMW bulb, rearward, & then reinstall the clip thing;  solder it, using a high heat soldering gun the cleaned & sandpapered new socket metal. I prefer this to the original pressure contact method ...which you could still use if you wanted to ...& I have found that also adequate ...although you will have to do a bit more hand filing it requires a slightly flatted area.

I'm often asked about what turn signal flashers to use if the old one is bad.  The following is copied from   NOTE:  the article itself has the latest information, the information below may not be the latest.

The /5 bikes use a 2 terminal thermally operated flasher relay unit.   It is load & voltage supply dependent; flashing speed also varies with alternator output (rpm).   An acceptable substitute is the Tridon Stant Electronic Extended Life Flasher 12 Volt, 2 Terminal  EL12.   Actually, almost any of the many available two-terminal flashers will work OK.

After the /5, the stock electronic flashers are complicated internally.  There are three different uses of these flashers.  One version, used on 1978-1980, had terminal KBL on the flasher connecting to the single dash indicator lamp.   Another version has the single turn signal indicator lamp connected from the left lamps to the right lamps, & there is no usage for a KBL type flasher output.  The final version has two separate turn signal indicator lamps, such as on the R65, ST, GS type of instrument pods. The BMW flasher is rather pricey, & has special indication when a lamp burns out.   Much cheaper substitutes that are perfectly OK, are just about any car type electronic flasher, such as a Tridon, from the auto-parts store.  These 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 was 550, which is a thermal flasher, but handles the BMW lamps just fine, & would even handle extra lamps, such as on a trailer or hack.  An electronic flasher could also be used. Connect the P terminal to the indicator lamp (usually a green wire); the X terminal to the power (old terminal 49 wire, green-black); & the L terminal to the load (old terminal 49a, green-yellow).  If you have two INDICATOR lamps, don't connect to the P terminal.  It is possible to rather easily add a piezo tone unit to any of the flasher setups.

For those of you that intend to use LED lamps for flasher turn signals, aka trafficators, you may have problems such as all 4 flashing, or some flashing dim, on the wrong side of the bike, indicators flashing wrongly, too fast flashing, etc.  This is all due to the LED lamps not having the current draw of the original incandescent lamps.   While I have listed a few flashers, above, and you are referred to my electrical hints article by the link, above, here is a place where you can not only purchase lamps, but they have full electronic flashers that do not need load resistors. They also have quality load resistors if you need them:

05/11/2003:  Add .htm title.
05/14/2003:  Editing for clarity.
06/23-24/2004:  Modify instructions for bikes using single bulb rear tailight unit; clarify in various places to cover all models, and upload to Internet.
03/23/2006:  Minor updates...mostly clarifications.
05/06/2009:  Rechecked, and made minor clarifications again.
05/25/2009:  Add the California 24603 V.C. information, inadvertently left out a long time ago.
06/08/2012:  More information regarding the Euro lamp 7528, etc. Add hyperlinks to my lamps article.
09/10/2012:  Slight updating inside article.  Add link; add QR code; change Google advertising layout.
04/27/2013:  Revise the entire article for clarity, but with only MINOR technical information changes.
10/04/2014:  Clean up some.
12/20/2015:  Update meta-codes; revise article for left justification for smaller screens; larger font; clean-up.
05/01/2016:  Final updates to meta-codes, layout, justification, etc.
09/01/2016:  Add note in red about LED lamps and flashers.
11/13/2016:  Clean up html.
11/20/2017:  Reduce colors, fonts, excessive HTML.

Copyright, 2017, R. Fleischer

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Last check/edit : Monday, January 15, 2018