I have 78 gt. The indicator lights in dash come on when you turn on lights. I have new light sockets front and rear with new bulbs. Wondering why the lights come on. Indicators still work.
That means you have a ground that came off or is broken. Check along the core support in the front of the car and you will see some ground wires there inspect them. Also make sure that the core support has a good ground going to the battery. Next check the grounds for the tail lights.
I am watching this thread because my marker light, just one of them, come on when the parking lights are selected but when the headlights are selected the marker lights are off like normal. I suspect the switch but my wiring is 50 years old so that is also a possibility
It sounds like the slider in the switch is coming apart, getting stuck between two leads in the switch, or the lead is loose and pulls along with the terminal with the slider. It's been a looooooong while since I handled a '60s Ford headlight switch; could it be taken apart without destroying it, such as drilling out a rivet?