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I had the same problem on my 77, tried the headlight switch (easier and cheaper) no luck. After looking for a gauge cluster with a good printed circuit board I decided that my lighter worked just fine. They are hard to find and apparently they are made with gold or some other rare precious metal. I know this isn't what you wanted to hear but I still have some feelers out looking for the circuit boards I'll let you know if I find one.
Look for wires pulled out of the harness somewhere. Mine *were* working and stopped after I changed the ignition switch and headlamp switch. Go figure! I did find a few wires laying around unconnected and I think I might have shorted something out.
The wires I found unplugged are a yellow with black strip and a bullet connector with two brown wires. Since my rear lamps and dash lamps no longer work, I suspect each wire controls one of the others.
I would look for wires leading to/from the headlamp switch.