'77 r100rs electric issue

Just returned from a ride and discovered: rear tail light/brake light out, rear turn signals out, front turn signals work, turn signal indicator flashes once, then out. Literally just walked in the house, so I don't know if bulbs are burned out, but I doubt. Any thoughts?

Sounds like problem with wiring harness to rear lighting, most likely the grounding (brown wire).

turn signals

The turn signal indicator light blinking once and then going out is the bike's way of saying that you have a bulb out. However, the chances of all of them going out at the same time is astronomical. I would bet that tail end wiring connector (just behind/under the gas tank just ahead of battery on my '78 R100/7) has come loose thus the bike "thinks" that the rear turn signal bulbs are out. The ground back from there also could be cut/broken/detached.

If you have a test light - connect the one end to the battery positive side, and then poke the brown wire or the ground inside the lens of any of the lights in the rear and you should get a complete circuit and the test light should come on.

Do the reverse to check each of the "positive" wires - connect test light to the negative, and then poke each of the positive wires/inside the lights and you should get light when the appropriate light is turned on.

lkchris said:

Sounds like problem with wiring harness to rear lighting, most likely the grounding (brown wire).

Click to expand...

Problem solved, connector under tank going to rear lights had disconnected. Probably should have done a little self-diagnosis before cluttering up the forum!