An Electrical Head Scratcher

barny

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I have a R100GS 1995 which has an interesting electrical problem. With the ignition on, if I apply either Front or rear brake the headlight side light and tacho and speedo lights come on. I have spent the morning with the tank off disconnecting cleaning connectors and earth points but no change. I am not sure how long this fault has been present it may have been for some time as I normally ride with the lights on so the fault is not obvious. Bits of a pun but can anyone "shed any light" on this or offer any help. I looked at the wiring diagram and there does not seem to be any interconnection between the 2 circuits.

Barny
 
Sounds like a grounding issue.
Also check the wiring loom around the headstock for chafing.
Good luck.
 
On the Rear light as a test

connect a wire from the brown wire where it joins the stop lamp at the tail light

to the battery NEGATIVE then try it again

There is a common connection its the brown wire it serves both

If your problem then disappears You have a bad earth connection or possibly a nipped wire in the loom
 
Please let us know how it pans out.

I am no electrician but I agree with Aberdeen Angus, as soon as something really illogical occurs, the earths are often to blame.

Good luck sorting it.
 
On the face of t, it sounds like an earthing issue, the earth being the only "connection" between the circuits. Dr Farkoffs test is a good one. While you are about it, carefully check the condition (and resistance) of the main battery to chassis earth lead - these were never the best quality and if its the original one by now it can easily have degraded and cause all sorts of weird issues.
 
Now solved.
It was self inflicted, I have recently fitted a Chinese LED rear light to make me easier to see me at night and it is this which is creating the earth problem. The LED light has a 3 wire connection identical to the BMW one, wiring is correct but for some magical electrical reason this is affecting the side and instrument lights. As luck would have it I terminated the BMW rear loom at the rear end with a simple 3 pin plug and terminated both lights the same to suit it if needed at a later date to revert to the original light. So I unplugged the LED plugged in the original light and all was well.

So many thanks to all for your input which was much appreciated, although collectively you did not solve the problem due to poor evidence on my part you certainly pointed me in the right direction again my thanks for your help one and all. Final conclusion when I am riding the fault is not a problem as the lights are on anyway I will continue to use the LED light for reasons of safety as I live in tractor county and street lighting although available in the 19th century is yet to reach Norfolk so I need all the help I can get. I will hopefully find a solution for the wiring in near future, I will see how others have fitted LED lights.

Good Christmas to all

Regards
Barny
 
[for reasons of safety as I live in tractor county and street lighting although available in the 19th century is yet to reach Norfolk so I need all the help I can get.

Good Christmas to all

Regards
Barny


No street lighting, but fast tractors. Glad you've got to the bottom of it.
 
I'd be ditching the dodgy LED as who knows if it will be failing when you need it most. The unit from motorworks works great and I have 100% confidence that it's doing its job as I ride.
 
Fecking LED lights again.:blast
More trouble than they're worth.
I just wish that people would state that they've fitted LED units when they first ask for help with lighting and indicator problems.
 


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