I believe ground is to the case. and positive goes thru two different wires to the hot sides. There are two hot wires i think so the motor can turn in two different directions. One on the up side comes off the cylinoid and the down is a direct shot from your down switch. Look for the positive wire leaving the cylinoid (sp?) and try jumping it directy from there and the case.

Try jumping it and tapping on the motor with a mallet. I bet its just bad burshes. I got some insert brushes at my local starter repair shop a few years ago and had mine fixed in an hour. I think there are two long bolts thru the motor that need to be unscrewed and then the motor comes up and off.

Conrad