All my electrical woes.

The radio is wired wrong. Yellow wires are dome lamp among others, but not the radio. If your car has a interior light timer tied in with the ignition lock cylinder, that's why the radio comes on when the key is inserted.
The voltage limiter is inside the fuel gauge.
I dont know where the tach gets 12 volts but since it and the limiter, and the blower motor all get 12 volts at switch on, thats a clue to where the new problem is.
I have 70 model wiring diagrams and I'll help any way I can. You'll have to promise you wont pinch any more wires LOL