That ground wire is open? Take a multimeter, set it to measure resistance. Disconnect that ground wire, measure the resistance of the wire to ground. It should be zero, short, or however your meter displays that.

If that wire is broken somewhere before it gets to ground, you'll see +12v in it while you're trying to start it.

Or.... Don't trust that ground wire, run a whole new ground wire. If you want to ghetto it just for a test, connect a wire from that ground over to the (-) battery post.