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R1100RT-P Tail lamp not working. Help!


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I got 2VDC eek.gif - not 12VDC as needed - on the hot side of the fuse for the tail light and the fuse is good. The headlamp switch turns that 2VDC on an off. The headlamp works as advertised, as do the brake and turn signal lamps. I monkeyed with the switches, but am reluctant to tear into them without some idea as to what or where to look. I am a retired Navy Electronics Technician, so can handle the troubleshooting, but thought someone here might be able to throw me a bone and save some time. Any constructive thoughts would be appreciated.

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Andy Johnston

On a standard RT the stop and tail lights are fed from the ABS control unit and would show a brake fault if either of the lamps are faulty



There are three switches between live/positive and the fuse F2 they are, load relief relay, light switch and the ignition switch



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stop and tail lights are fed from the ABS control unit and would show a brake fault if either of the lamps are faulty


Interesting! But not conclusive, dammit! I probably should have disclosed that my ABS is out, and the lights consistently flash on the dash, first one, then the other in sequence. I bought the bike a couple of months ago with this tic intact. The manual says this is what it looks like if the ABS is not working, and the mechanic at Morton's BMW in Fredericksburg, VA told me if I don't need the ABS it won't hurt anything. (I hate having control of anything I'm driving or riding taken from me, so I thought the ABS being out was a bonus.) The brakes and brake lights work wonderfully, and it passed the state safety inspection with the ABS light flashing away. I have replaced the ABS switch recently, but that did nothing for the ABS except stop blowing the ABS 3.5amp fuse. Could that switch affect the tail light?


I did check again, and the stop lamps are still working fine, so the 12V is there, just not getting to F2. Anybody got a wiring diagram for a P-bike? The site that advertises them asks for a dealer code.

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First off, I dont think (nor does the bmw schematic for the R1100RT) that the tail and or brake lights are in any way connected to the abs (r1150rt yes, r1100rt no).


Discounting the abs connection for the moment, where to look.


First, since you tested only 2vdc, did you use A: a good meter and B a proper ground? Yes, basic stuff, but so easy to make a mistake with. DAMHIK…


Second. The taillight can be switched on in two ways, one is the normal way, with ignition and light switch on. As mentioned by Andy earlier, this provides power from the battery, via the loadshed relay, via the lights switch, through the ignition switch before arriving at F2.

A nice test here is to test F4. this gets power from the loadshed relay, from the same connection which goes on to the light switch.


The second way is by locking the handlebars and turning the key on position further. This gives you parking lights. In this position only the tail light and the position light (the little 4w bulb) in the headlight are switched on.

Power here, is delivered from the battery, via ignition switch to fuse F2.


So, what to check? I’d first see what the parking light position does, whether you do get full voltage in that posititon. This give valuable information on the location of the problem.


Another thing to consider is that you have a RT-P.. who knows what may have been done to the wiring..


Hope this helps.. Daniel

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Just for sh!ts and grins, jump the hot lead to the brake light from the fuse panel then to the switch on the master cylinder and see if you have a nice bright brake light. If the brake light works well with the jumper attached to the master cylinder switch then the problem is between there and the bulb. If not it is between the fuse and the master cylinder switch.


If so, look at the wire leading to the lamp assembly or to the brake cylinder carefully along it's entire length. I'll bet you find a break in the insulation and moisture causing corrosion to the multi-strand wire. The remaining few strands are acting as a resistor... thus just 2 volts.

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Anybody got a wiring diagram for a P-bike? The site that advertises them asks for a dealer code.


I posted this address in another thread for manuals on the 29th. Hopefully it worked.




type this in you address bar, do not cut and paste. Whenever i do that that it ends up asking for dealer codes. Don't ask me why. I am using IE7 & Mozilla and it works with both.


Let me know if you have success.




Steve wave.gif

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