1979 r100rs electrical problem

[eriojas]

Hello, restored a 1979 r100rs, everything worked perfectly, suddenly, horn, alternator meter, brake light, blinkers, stopped working, any ideas? It starts perfectly, clock, rev counter also works perfectly

 

[Larry Langford]

Hello, restored a 1979 r100rs, everything worked perfectly, suddenly, horn, alternator meter, brake light, blinkers, stopped working, any ideas? It starts perfectly, clock, rev counter also works perfectly

a wild guess would be, possibly, an open rotor in the alternator ...... On my 73 airhead, I found that the rotor excitation current goes thru all sorts of stuff and then series' thru the rotor. Also check the switch and look over the wire loom as well. could be lots of things lose grounds .... you know .....
I had to get a new epoxy coated rotor for my airhead. This seems to happen to a lot of them, and if the rotor doesn't have the epoxy on it then you know it is stock ..... more on installation if you find that's it ....

 

[scooter paul]

On this model and year does the handlebar switchgear wiring join the main loom via multi block connectors at the headstock? This sounds suspiciously like one has become ( slightly) disconnected possibly by tight wires being pulled by handlebar movement on full lock.

 

[mikeyboy]

On this model and year does the handlebar switchgear wiring join the main loom via multi block connectors at the headstock? This sounds suspiciously like one has become ( slightly) disconnected possibly by tight wires being pulled by handlebar movement on full lock.

No,all of the sub harnesses run into the headlamp on this bike.
At the back of the headlamp bowl there is a combined distribution and fuse board.
Maybe the inoperative systems share a fuse?
The correct wiring diagram would be very useful to understand how things are connected .
Despite how it looks inside the headlamp it’s actually fairly intuitive once you get to grips with it.
On a uk bike I’d suspect corrosion to be the culprit but the OP appears to be in Mexico so who knows?

 

[Larry Langford]

No,all of the sub harnesses run into the headlamp on this bike.
At the back of the headlamp bowl there is a combined distribution and fuse board.
Maybe the inoperative systems share a fuse?
The correct wiring diagram would be very useful to understand how things are connected .
Despite how it looks inside the headlamp it’s actually fairly intuitive once you get to grips with it.
On a uk bike I’d suspect corrosion to be the culprit but the OP appears to be in Mexico so who knows?

Yes a clymer manual wiring diagram is crucial for this kind of work. I managed to fix my open rotor (electrician), but I had to borrow a puller from a BMW shop mechanic, paid with a fifty dollar case of imported beer that was requested. But It might be a tad difficult for someone just learning DIY imo. When the rotor opens, several things go down that are wired to the excitation current circuit, making it look like a plug came apart too. But it could be just a loose ground somewhere ....... who knows.

 

[Helibatics]

I had the same issue on my R100s. In my case one of the fuses in the headlight bucket was a bit corroded. Once cleaned up everything worked again.

 

[Gelandestrasse]

The ignition switch when switched on moves +12V via a green wire to a fuse on the terminal board that supplies all circuits that use a green/black wire. Conveniently these circuits are the turn signals, volt meter, horn and brake lights. As Helibatics mentions #6, cleaning the fuse can cure it, even rotating the fuse in its holder without removing it can remove the corrosion. If the fuse is blown, proceed with caution as one of the circuits has drawn enough power to blow the fuse.

If the alternator rotor is bad, the GEN light will stay on.