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

Either !!!! There is some tremendous load somewhere during crank that is causing a massive voltage drop OR there is a bad connection in the brown / bypass circuit or bad ignition switch

You should be able to run this down quickly.

With everything normalized, measure the power at the brown/ IGN2 at the key switch connector, compared to the coil. If that is good, it almost has to be the bulkhead connector. This is a simple circuit. Goes from IGN2 at the key, through the bulkhead, and to the coil side of the ballast.

If that doesn't work I simply don't know "without being there."