Having problems with my running lights and dash lights on my 1993 F150. When the headlight switch is in the off position, the dash lights are on full bore (turning the dimmer has no effect). When I turn on the running lights/headlights (either position) the dash lights go out and the running lights do not work (headlights work fine). All the fuses are good as well as all of the lamps. Replaced the headlight switch 2x and the problem is still there.
Any ideas on what might be wrong here?

 

Do you have a trailer plug or after market lights or any additional elec things added? It sounds like a short somewhere.