I would pop the bulkhead connector and check for more damage.

What you describe would full field the alt. Causing a serious over charge. Normally I would expect the feed line to burn, not the sensing/ign wire to burn.

Carb is not at rault. It is an electrical issue.

Regardless of how un hacked the wiring is, you still need to look it over now starting with the big wire at the alt all the way through the firewall.