I just got my truck all back together, and it finally runs after 2 months. However, I've got a bit of a problem. With everything off, there is a draw from the battery of about 8amps. With it running, its about 15 volts at idle and 17-18 revved a bit. When I take the cable off the alternator (engine off) the draw from the battery goes away, regardless of whether the plug in the back is connected or not. Is my alternator/ regulator toast? It was working fine before I did the frame swap/SAS. Any ideas appreciated.

1989 3.0 5 spd extended cab with more rust than should be legally aloud, soon to have a D44 front and D60 rear