CaptainMo,
I'm not a GMC guru, but it sure sounds like you had it hooked up backwards.
I'm pretty sure the standard polarity connection for a GMC your year was POSITIVE ground. Although battery cables can get swapped all over the place by unknowing folks, the battery has a large post which is POSITIVE, and this would make sense to be connected to a red cable, which should go to ground.
Your problem sounds like too much voltage for the ignition system, but this could be exacerbated by wiring it backwards.
The wire from key to coil would attach to the -, or negative side of the coil if the rig were wired for POSITIVE ground.
The ammeter would show a constant discharge if the thing was wired backwards too.
I would try the six volt battery, with big, adequate cables and make sure to attach it NEGATIVE post to starter and POSITIVE post to frame/engine/ground.
A new set of points and condenser would probably get you going again. The coil is probably OK, but headlights and other little lamps and gauges don't really dig all that voltage.
Again, I am not sure on this, but I think it's right...good luck.
Stuart
