Reach in with a finger nail, pull back the springs which hold the brushes against the commutator and let them snap into place.
I had one that stopped charging midway of a 1,000 mile trip. I did just that and it started charging. I put 15,000 miles on that truck after that before I parked it for 18 years. After that 18 years, I charged the battery, and cleaned the points. It started up and purred like it always did and the ammeter showed a charge.
Dirt must have bound up the brushes. Once the brushes wore just enough to not make contact, it stopped charging.
Carl
