65 Dart Instrument Voltage Regulator Tips

Looking at the wiring diagrams, I can see that the wires from the Alternator Gauge go through the firewall connector, the red goes to the starter relay battery connection, and the black goes to the output of the alternator, so perhaps I've lost ground somewhere else?

This all happened after I disconnected the headlight switch from the wire in order to inspect it and see if I should order a new one, after unplugging it and plugging it back in everything has been dead.