Most likely the potentiometer that controls the dash lights is either worn or dirty. It would take a replacement headlight switch to fix it. You might be able to remove the switch and clean the coils on the potentiometer. Picture has an arrow pointing at the potentiomenter. Replacement switches available from Jim Carter. LINK
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Headlight switch.jpg (14.62 KB, 208 downloads)

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.