I know "motoring" is a quick way to test them, but what I did to test mine is to cut the head off the right size bolt and (with the pulley off) screw one end into the powerhouse and chuck the other end in my electric drill. When spun up it put out 18 volts, so I guess one is good to go. The other put out less then 1 volt so I'll have to go through it. First checking for shorts in the armature and field coils. then replace the brushes. Unfortunately powerhouse generator parts (other than brushes) are not common. So do everything you can to save the original parts.