Electrical issue

[Bombayduck]

Hello everyone. I

was a member back in the 80's. This is a 70K R100S that I recently bought. It has a number of issues that I'm sorting out. The bike is very rideable and while starting my ride today, a few miles out I noticed my volt meter has stopped working. It's been erratic (have to tap on it to get it to move sometimes). Also, no turn signels, horn or brakelight. The headlight low and high work OK, the taillight is OK and the clock works as well and the engine lights, are all working. Starter works too. I checked the fuses in the headlight bucket and checked out OK in looks and continuity. Checked all the bulbs in the turn signels and stop light. All OK.
I have a newer battery and the voltage at the battery is 12.8 while the voltage inside the headlight bucket is 12.25. That seems like a lot of drop off. Any thing I should check for?

Thanks

Brad
(back in thr saddle again)

[Bombayduck]

Forgot to add it's a 1981

[20774]

Most likely your problems are poor grounds given that bulbs and fuses check out OK. The horn is pretty simple. Power comes through the horn button switch and goes to the horn where it is most likely grounded right at the horn. So, I would follow wires and check the grounds.

You might also have some corrosion in the switch unit that has the turn signals and horn. IIRC, it can be "interesting" to open that up and service it....parts might fly away to unknown places.

As for the battery reading difference, yes it's possible to see that much of a difference between the battery and where it is plugged in at the headlight shell. You can just use this ~0.5 volt difference and add it mentally or reroute the battery wiring directly to the battery. I've done that on my /7 and have a waterproof switch on the power side to cut off the power drain when I'm not riding.

[Bill Burke]

If you did a visual and continuity check on the 8 amp fuses but didn't remove, inspect, clean the fuse ends to shiny, apply a little dielectric, and run a little rat tail file into the fuse holder prongs to clean up the holders, I'd recommend you try that. It may still be a fuse issue from the sound of the symptoms.

Edit: Belay my last. See below. Glad you found the problem.

[Bombayduck]

Found it. It was just south of the horn wire connector where it splits up to go to the left and right horns. A broken wire there. Thanks Kurt

[Bombayduck]

Thanks bill, I'll do that also. Now I have to get some spare 8A fuses...

[Bombayduck]

OOPS It came back again. It was in the wire near the connector for the front brake switch not the horn connector as they look the same. It looked like the wire was cut part way through so I bared the wires and used solder to fix it. Then it all worked ok and then I tried it again and it was back the way it was again. By the way, I checked the front brake switch by checking continuity in the connector with the brake pulled in and the switch is OK. All was working even with the brake wire connector unplugged and then it showed the same symptoms. The fuses are still OK, none blown (yet). I guess it's an intermittant ground somewhere along the wire/ circuit? I hate those! Anywhere else I should look?

Thanks

[Bombayduck]

There is some partial continuity between the connector prongs in the connector that goes from the brake switch to the rest of the circuit witht the key switch off. I don't think there should be any or am I wrong about that?

[Bombayduck]

The fuse (the one on top) which looked good and tested good was not. It blew when I rotated it to check the connection. I put the bottom fuse in the top location to test so now the circuit works right again. I guess the lesson learned here is that even if the ceramic fuses look good and check good, they can still be a source of trouble.

[Bill Burke]

Belay my last belay. Glad you found the problem, again. Cheers.

[amiles]

I hope that you have solved your problem. As it was intermittent I was suspecting your ignition switch. Should the problem recur, try working the key around a bit as though you were trying to pick the lock to see if the contacts are wearing out/dirty.