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Greetings

Could use some electrical help. I have a 1976 R75 with stock electrics except for a a Sorenson voltage regulator ( auto type). Everything was working okay until I had to replace the light/dimmer switch. I did this after the headlight would not work. The replacement switch had same color coded wires as original except for the hot wire (red) which is not included in the replacement switch (purchased from BMW dealer). The new switch also has a green/black wire that is not part of the original but comes with instructions to attach to the brown coded section of the pin plate in the headlight bucket.I installed and got headlight back and front right/left blinkers working. Now the weird part, with headlight switch on for lights, the rear stop light blinks with the turn signal on. I rechecked my wiring connections with a good wiring diagram pulled from other posts and everything seems to be connected correctly. I even tried to connect the new green/black wire from new switch to the red connection pin on the pin panel (position 30) used on the original light switch. I also replaced the blinker relay and light relay, all correctly reconnected with proper wires (compared them with my R100S). Anyone run across this issue replacing the headlight switch?

Found the problem. I added a jump wire from battery negative to ground connection on tail light and everything worked normally. Must have been a grounding problem somewhere in the tail light that was allowing current to leak when flasher is turned on. I did not have this problem when original light switch died but maybe something got knocked loose during my repairs Now I can concentrate in tracing the bad ground. Hope this helps anyone else experiencing weird electrical problems.

Thanks

Greyhead, that is is good news. When I saw your post yesterday I dug out my electrical diagrams and pondered your problem. Couldn't come up with any useful suggestions and hoped that someone else would chime in. Welcome to the forum, by the way.

Welcome to the forum, greyhead. I take it your name refers to the grey heads on our Beemers.
Nice way to isolate a grounding issue too.

Check the main harnes/frame ground. That is the 2 brown wires that join together through one eye connector on the RH ( I think ) coil mount. Wiggle those wires while your lights are on and see what happens. Probably best to replace the connector.

The front signals are the only bulbs that ground to the frame, all the other lights ground through the harness to the coil mount. If the frame ground is bad the only other path is through the front signal lights to ground. When the headlamp is turned on, it can't find a ground so it grounds through the tail light bulb which shares a ground with the rear turn signals. The power passes through the rear signals up to the front signals and then finds them grounded. As a result all the lamps glow dimley.

Don't ask how long it took me to figure it out.