72 Fury III buzzing noise in dash

Make sure your headlight and turn signal ground wires up on the core support are making good contact.

Clean them up. Most of these cars are 50 years old, clean all your electrical connections.

When electricity can't get back to the battery though a good ground it backfeeds and does all kinds of crazy things.

Electricity follows the path of least resistance. And if that means going through all the wires in your dash to get back to ground so be it.

Pull all your fuses out too and clean them and their holders up with scotch brite pads for good connections.