Firewall Bulkhead connector - #1 problem on old mopars. Too much juice going thru the heavy black and red, from the battery and the alternator, and they get moisture in them, corrode over time, cause resistance and heat. Trace the heavy black and red wires to the connectors, disconnect the battery, remove the connector, remove each wire one at a time from the connector, wire brush clean, grease with dielectric grease, reinstall in connector. Bypass any melted wires with new connections in the engine compartment and on the corresponding backside of the harness inside the car.
EVERY old mopar I work on I do this, regardless. Makes a world of difference for reliability sake.
Male connectors can be removed by bending inward slightly to release the barb/hook that captures them. Bend back before reinstalling. Female connectors are trickier, they have a barb/hook on the flat side of the connector - a very thin screwdriver or paper clip can be pried in to bend the barb down. I take a dremel with a wire wheel attachment and shine the connectors up.