Instrument Lights Not Working

It certainly sounds like a feed since none of the lights work. I`m not familiar with your instrument panel but I would guess it does (like most all other Mopars of the vintage) have a voltage limiter on the instrument panel. 2nd generation Barracudas have them located in the fuel gauge, I don`t know if yours does or not. Does it have 2 or 3 terminals on the gauge. If 3 it may be in the gauge. When you locate it you should have 12 volts going in it and about 5 volts coming out. The voltage will be intermittent because there`s a bi-metal switch inside the limiter that heats and cools causing a strip of metal to bend and break the circuit and cool to complete it. The result is a 5 volt average (pulse) that feeds your gauges and maybe your lights. See if you can find a schematic of your panel and trace the incoming 12 volt feed from the fuse box. I wish I could help more, I just don`t know your cars dash that well. Let us know what you find.