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850T-3 Not Charging

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Piston Broke:
Greetings! During my first ride this year, my '76 T-3 died due to the battery not charging. Unfortunately I have never been good with electronics, my brain just doesn't work that way i guess. Anyway, I could use some help troubleshooting the issue. Thank You!!
She ran quite well last year...
The battery light stays on while the engine is running which indicates an issue.
I measured 4 volts at the screws where the alternator brushes attach while running.
There is no continuity between the two rings when the brushes are lifted up.
How do I test the regulator? How could it possibly go bad during the winter?








 

moto-uno:
  It seems you have a common high mileage charging problem and you've already found the problem .
No continuity between the rotor rings means the winding in the rotor is broken and no magnetic field can be produced .
It is a single wire that is wound around the rotor and each end comes out to it's own rotor ring .
I've had some entertaining time rewinding a couple of my own  :grin:.

guzzisteve:
The best trouble guide is in the 1000SP/G-5 service manual- I would read it

moto-uno:
  ^ Or start with a rebuilt or new rotor .

wirespokes:

--- Quote from: moto-uno on May 27, 2026, 11:08:10 AM ---  It seems you have a common high mileage charging problem and you've already found the problem .
No continuity between the rotor rings means the winding in the rotor is broken and no magnetic field can be produced .
It is a single wire that is wound around the rotor and each end comes out to it's own rotor ring .
I've had some entertaining time rewinding a couple of my own  :grin:.

--- End quote ---
I'd be interested in your rewinding adventure. I never thought of rewinding any of mine that failed, thinking it was beyond my abilities. But thinking of it now, the only real problem is baking the epoxy. That, and maybe removing the epoxy to get at the wires.

My understanding is that most of the failures are where the wire connects to the slip ring. The winding starts loosening up from hard acceleration/deceleration working the connection till it breaks.

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