72 Ignition wiring gets hot

[Supertommy68]

I have a 72 Cheyenne Super 4x, 1/2 ton, 350/TH350 and some questions-
first, Years ago, put Mallory unilite in with promaster coil. Ran the original coil wire to the new coil way back when. The wire gets real hot when the key is on (not running). Like melting hot. Why? Its been melted so many times I have cut it back to where its only 6" sticking out at the firewall and spliced.

Second, I have a new replacement harness (form LMC). This has the yellow wire coming from the starter, which looks like its supposed to go to the coil. I am ditching that Mallory and promaster and am putting in an HEI. Does this yellow wire power the coil? Or do I hook up to the wire that gets hot when the keys on?
I have a rats nest of wires, hence the replacemnent harnesses. Any help is appreciated. I don't want a fire.