If you have a volt meter, check for AC voltage at the yellow wire going into the regulator, if you can get to it. If not, the yellow wire coming out of the motor by the stator. it should have 12-13.5 volts at 2000 rpm or more. if not, the lighting coil might be going out, or the regulator is dumping all the voltage to ground. I know its hard to check it cold, as it seems to work as it warms up.