72 Dart Swinger has melted wiring under dash?

What makes you think "melted" AKA did you see smoke, etc? Have you examined some of the harness and it LOOKS melted?

First see what if anything works. If it wants to smoke, then put something like a tail lamp or head lamp in series with the battery ground. This will allow you to test it live

Look for the fuse link and see if it's "blown." It goes from the big stud on the starter relay to the RED wire in the bulkhead connector, out in the engine bay

Go to MyMopar and download yourself a free service manual. I think the 72 manual over there is Plymouth, not Dodge, Very little difference, except trim

Then come back here and we'll "play"