The generator light.

[Jean]

Irz, ther's a little diode on the back of the diode board that can cause this, when it gets snakey.
Also, dirty/corroded connections in the rotor charging circuit.

[dougie]

Rick at http://www.motoelekt.com/ used to sell an appropriate resistor already pig-tailed and shrunk wrapped with instructions. I can't seem to find it on the website now.

[Rob Frankham]

What exactly does your gen light do?

Apologies for the delay.

Gen light glows very faintly as in waaaaaaaaay less than 1/2 brightness, glow brightens a bit w/ rpm increase to 4k or so at which point it goes dark.

An rpm drop below the "no-glow" threshold results in...a faint glow.
Pretty classic situation based upon my internet research.

Very likely to be a failed diode on the diode board. Any single diode failing will give this symptom. There should be a testing procedure at http://robfrankham.co.uk/index.htm but that seems to have disappeared. If it doesn't reappear in the next day or so, I'll redo email it to you.

There are other possibilities but, with evereything else you've done, thats favourite.

Rob

[SteveD]

Great video showing how to troubleshoot when the GEN light fails.

https://youtu.be/oxQwx5EC5X4

[Rob Frankham]

FWIW, I've re-published my testing procedure for the diode board at https://robfrankham.com/diode-board-test.

Rob

[Gibson]

I had this happened on my 94 Mystic R100R. It turned out 3 of 4 rubber mounts were broken. Caused the board to be damaged and also took out my regulator. Very common. I replaced mounts with aluminum standoffs and replaced grounds. I used metal electronic rectifier from Euromoto. Charges better than ever. 14.4 volts.

[Gibson]

I had this happened on my 94 Mystic R100R. It turned out 3 of 4 rubber mounts were broken. Caused the board to be damaged and also took out my regulator. Very common. I replaced mounts with aluminum standoffs and replaced grounds. I used metal electronic rectifier from Euromoto. Charges better than ever. 14.4 volts.