No more instrument panel dimmer?

[MopaR&D]

The other night while out driving my '70 Duster the instrument panel lights all of a sudden went out. I thought it was a bad fuse but a new one didn't fix it. I then found that the panel lights would only work if I turned the headlight switch all the way to the left. What happened, and how can I fix it? I put in a new headlight switch not too long ago so I hope I don't have to get another one.

 

[cudajim]

Yup, you probably blew out the dimmer rheostat in the headlight switch. It's just a variable resistor, also known as a potentiometer, which drops voltage across it and the result is a lot of heat which has to go somewhere. Usually it ends up frying itself but it's not a real common occurance . Pull it out and test it on the bench with an ohmmeter. It's a 3 terminal device; 2 ends of a coil with a center wiper to pick off voltage at various points. The resistance should vary as you turn it. Also, you should have a fixed resistance between ends of the coil, I am guessing less than 100 ohms or so. Double check your fuses too.