Why not cook marshmallows on my under dash fire?

Get a can of electrical cleaner, and only electrical cleaner, and spray away all the soot from the fire. Post some pics.

I wouldnt go so far as bypassing every wire on the bulkhead just yet.

I would go with the bulkhead main hot wire bypass. These days, Im not even powering up an old mopar without doing that first. And making sure my engine is grounded to the body. And the voltage regulator is grounded to the body. Those three will cause major headaches.