Hello.. m y son has a '74 and we just put a new wiring harness in it. We are trying to put a new radio in the car but the "always hot" wire is not hot and the "ACC" wire is only showing .20v whether the ignition is on or off... All fuses are good.. Sounds like a grounding issue to me but any suggestions? Thank you..

 

Welcome to the Club. You will have to run a hot wire from the BATT spade on the fuse panel because radios weren't 'hot' wired back then.
As far as ACC, check fuse panel input from IGN switch as IGN switch controls power, check RADIO fuse and ACC spade for ACC power. Ignition switch could be wired wrong.