It could be a lot of things. Start with checking stator resistances. You can find them on the attached diagram. Y to Br is the coil that feeds your lights and handwarmers etc. It could also be a short circuit to ground on any part of the lighting circuit. A common trouble location is where the tail light wiring goes under the seat the insulation gets worn off the wire and shorts it out. It could also be a faulty regulator.