Underdash Harness bunt up

I had the exact issue you're having on my 72 Charger. Whatever the cause I'll never know. Was it the old corroded wiring, or the poor firewall connections? ( I bought the car all burned up like that) So I have no idea what the previous owner had done.

I also did not want to spend $700 on a whole new harness. I found a guy at Mopar's in the Park last year that was selling used good harnesses. I think I paid $250. I can try and find his card from last year if your interested.