Time to remove and repair, possibly replace, under dash harness

DON'T DO IT !!!!
Those terminals are usually the ultimate source of the over heated wires - corrosion between the two parts of the terminals. Taking the bulkhead connector apart is pretty easy and it's as much work to do the splice as to put on a new terminal. Pack the bulkhead connector with dielectric grease when you get ready to put it all back together.

I would especially suggest to you that you get a new underhood harness (everything from the firewall forward) even if you decide to rebuild the underdash harness yourself. Think about it - the dash harness is inside your car and away from extreme heat, where the wiring under your hood is outside and in an enclosed space with your engine and exhaust.