63 Valiant Wiring Harness

I just bought a 63 signet convertible. I pulled the instrament cluster out and found the wiring harness fried. The main red and black wires to the ammeter are melted and have exposed wires, which was surprising because the car starts and runs like a dream. I have two questions: 1) what would cause this? It looks like the car has a new alternator, I was thinking that could be the issue. 2) where can I get a replacemnet or reproduction under dash wiring harness? There is no way to repair the damage to the existing harness, the wires are melted throughout. I'm surprised the car never caught on fire. Any help or suggestions are greatly appreciated.