Tail lights, dash lights

What do you mean by, "radio quit"? Do you mean it is dead, or the face plate lights do not turn on with the dash lights? When you replaced the head light switch, did you see any black or charred terminals, or any part of the connector body was melted?

Which engine do you have? Do you have one or two head lights on each side? Do you have daytime running lamps?

If you have a pink/red wire at the head light switch, check if that has twelve volts. For best accuracy, back-probe the wires with the switch plugged in. If you find twelve volts, turn the switch on to the tail light position, then see if you have twelve volts on the black/yellow wire.

I suspect you're going to find with the original radio that the display does not dim when you turn on the running or head lights, and the display brightness doesn't change when you turn the dash rheostat.

These are all symptoms of a miswired aftermarket radio. Specifically, people will use an ohm meter to find what they think is the ground wire. The black / yellow wire reads real low resistance to ground, not because it's a ground wire, but because it's reading through the numerous tail and running light bulbs, hen to ground. Using that as a ground wire shorts that circuit to ground through the radio's case, then the antenna cable's outer ground shield. That will blow the tail lights fuse too.

The orange wire at the radio is for the dash lights. The black / yellow just tells the display to dim when the head lights are on. The orange wire is tied to the dash lights, and tells the display how much to dim. That one will also read very low resistance to ground through the many dash light bulbs. Using that as the ground wire can overload the dash light rheostat, or the radio will stop working depending on where the rheostat is set. When there's a separate dash light fuse, that will eventually blow too.

If I'm right, replace the blown fuses, then be sure the original radio works properly. If that is an AM / FM / CD / cassette combo radio, those are REAL high quality, so don't throw it out. I sell a lot of them at old car show swap meets for upgrades when people buy used cars.

If you go back to the aftermarket radio, the black / yellow and orange wires aren't used. The correct ground wire is a black wire clipped to the back of the radio, or a braided strap bolted to the back of the radio.