....Test a generator by running it as a DC motor. You ground the frame, hook the hot lead from the battery to the the armature and jump the field to ground and it should spin like a motor, lift the field and it should stop. We had TWO generators that would run without the field grounded. (Shorted feild) The result would be a full charge no matter what. JP Jul 2003 ==================================== First make sure and polarize the generator then with the car running put a volt meter to the battery with the engine around 1200+ RPM this should give you about 6.7+ volts, have a friend turn on the headlights that shouldn't drop the voltage more than 0.2 volts (and no drop in voltage at all is best) then do the same test at 2400+ RPM this should give you about 7.2 volts and do the same headlight check and watch for a voltage drop. Then proceed to what John Paulos recommended "Ground the field wire on the generator, if it charges like mad it's the regulator, if not, the generator is shot". Next, disconnect the belt and unhook the wires from the generator turn the pulley by had to feel for any strange noises, roughness, etc. If that seems to be ok take a charged 6 volt battery with the generator STILL DISCONNECTED (like the one in the car)! and using jumper wires connect them to the generator and then the hot wire to the battery then hold the other cable to the negative (USE RUBBER GLOVES or make sure your holding insulted wire) and KEEP EVERYTHING AWAY from the generator and the generator should run like an electric motor. If it doesn't pass the voltage test or the 'electric motor' test it likely just the brushes. But don't forget the basics, new battery or not check the water level of the battery first, a low battery can't hold a charge for very long. Hope this helps, by the way you don't have to do every test here if you've found the problem! : )\