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Started up my '72 R75/5 yesterday. I had stored it for a couple years after running it dry and draining the bowls etc. Fresh gas, fresh battery and it fired right up! On the first ride I noticed the generator light would go out at just above idle as it should, but then it comes fully on again at higher revs. I cleaned up the rotor slip rings, rotor tested good, and the brushes have plenty of meat left. Still the same symptom. Any ideas, before I start swapping parts?

The rotor might be going open once it's spinning, even though it tests good statically. Do the brushes slide in their housings? They might look OK, but if the springs aren't keeping them tight to the slip rings, you could get lift off at speed.

Kurt in S.A.

It could be good to check the connections on the regulator as well Tim.

I'm with Kurt...brush springs. Maybe are getting hung up at higher revs and not applying correct down pressure on brushes to slip ring contact. Maybe the brush pigtails are getting hung up somehow?

Rotor going "open" when spinning at higher revs is a quite common old age fault.
Rotor tests good at rest and has open circuit at common charging speed.
All the other things are good to do too, but usually changing the rotor is the best proof that your old rotor is dead.

Well, I changed the rotor. That didn't fix it. Brushes were about 1/3 worn, so I swapped them out too. No luck there either. While it was running, I happened to bump the ignition switch and the light went out at higher revs, so I wiggled the switch and got it to go on and off. Looks like I will be giving a go at trying to make better contacts in the switch tomorrow... What I don't understand though, how would a poorly contacting ignition switch make the generator light come on? Another question, how far do you twist the brush springs for proper contact? Should it be 1/2 turn or 1? The outer one was a full turn, but the inner on was only half.

If the rotor goes open, the light cannot come on as that is it's path to ground.

What happens to the voltage when the light comes on at speed?

Does your /5 has fuses? If they have corroded connections and/or the feed to them from the switch (58 terminal) or the switch contact is dirty, there is not enough current being supplied to run the other users of that circuit. As a result power comes backwards from the D+ side of the diode board, through the gen light causing it to glow.


Or not.

It's a '72, so it has no fuses.

I was going to suggest the diode board could be the culprit. You know how little I know of the 'lectrical stuff, though. I was just going to say that because replacing the diode board fixed the dim glow of the gen light on my RS.

Aloha, Chuey

Chuey wrote:I was going to suggest the diode board could be the culprit. You know how little I know of the 'lectrical stuff, though. I was just going to say that because replacing the diode board fixed the dim glow of the gen light on my RS.

Aloha, Chuey

Yeah, your dim glow is different than an intermittent light.


(see how I didn't have to do anything with "your dim glow?")