1985 K100 RT tail light

[DWEBB49]

I hope this hasn’t been covered before. I did make a quick search but I may have missed on. If so, apologies .

My tail light not working (again). I would appreciate any suggestions as to what is causing the problem.

I have exhausted my skill, which is modest.

Brake lights and rear signal lights function fine.

If I swap brake light leads to tail light, tail light works so bulb and socket are good.

Tried swapping out BMU with a different one , ( used )and also tried by passing by soldering jumper wires to old BMU as suggested by Snow Bum. No effect. I am taking it on faith that the BMU was working.

Checked and tested fuses - all good and power to fuse block.

Pulled the plug at rear of cycle and tested for power and no power to the black grey socket.

Tested continuity of parking lamp power and ground and checks o.k.

So somewhere between the fuse block and rear plug it breaks down and no apparent interruption.

Suggestions as to next steps.

Is there a way to by pass BMU? I tried the 3 jumper method but it did nothing.

 

[98lee]

Pull the bulb monitoring unit (BMU).
Go to the socket. Locate terminal 58E. The terminal numbers are on the bottom of the BMU if the socket is not labeled.
Check for 12v between terminal 58E and ground with the key on.

If you have that 12v, temporarily jump 58E and 58A in the socket. Turn on key. Taillight should light. If it does, BMU is bad.


Let me know what you find.