Busted84GT

This morning after work I started up my mustang and went to the gas station to fill up. I shut the car off and filled it and after that it wouldn't crank again. I pushed it out of the way and then got a jump. I drove it home and grabbed the multimeter and checked my volts on the battery. It was low and kept dropping until the car actually stalled out around 9 volts. It seemed to me as though the alternator was bad so I went out and got me one. I brought it back and realized that the one in the car is a one wire alternator and the one I got is not. I hooked up the one wire on the alternator and it doesn't do anything when I jump the car. What else do I need to hook up to to get it to work? It's an 84 gt and I can't find anything to help me out.

Busted84GT

Or maybe it's just my battery