Cranks but won't start. Unplug ground at field spade on Alternator and it starts?

The difference in field current could be brushes, and normal. If you look the field current test, in the alternator section of section 8, it shows hand rotating the alternator while measuring field current. This is because the brushes do not make all the great contact, stationary, and when rotating / running, sort of "average it out."