Instrument Panel Lights Not Working

[johncc]

I have a 99 Silverado and whenever my headlights come on, all the dash light go out, as if the instrument panel dimmer wheel is turned all the way down. If I turn the dimmer wheel all the way up until it switches on the cabin light, all the dash lights come on. Is this simply a faulty dimmer switch, or could there be another problem?

[DofD]

It does sound like it is a problem with the dimmer switch shorting out. I would start with replacing the dimmer switch.