WHILE OPERATING THE VEHICLE WITH THE HEADLIGHTS ON, A BURNING SMELL DEVELOPED. THIS WAS FOLLOWED BY INCREASINGLY VISIBLE PLUMES OF SMOKE WHICH EVENTUALLY IMPAIRED DRIVING VISIBILITY. FLAME WAS VISIBLE BRIEFLY. AFTER DISCONNECTING THE BATTERY POSITIVE CABLE, IT WAS DETERMINED TO BE A CLASS C FIRE AS THE SMOKE AND FIRE DIMINISHED. THE VEHICLE OPERATED NORMALLY AS LONG AS THE HEADLAMP SWITCH WAS NOT TURNED ON. UPON EXAMINATION BY AN AUTOMOTIVE ELECTRICAL SPECIALIST, IT WAS FOUND THAT A SPRING ON THE DIMMER SWITCH USED AS A VARIABLE RESISTOR HAD SEPARATED FROM THE SWITCH HOUSING MAKING CONTACT WITH THE FRAME OF THE DASH ASSEMBLY CAUSING A DEAD SHORT TO GROUND. AS THE SPRING WAS ELECTRONICALLY RESISTIVE BY DESIGN, IT GLOWED TO A BRIGHT ORANGE IGNITING COMBUSTIBLE MATERIALS AROUND THE SWITCH. THE LOCAL DEALERSHIP FOR THE AFORE MENTIONED VEHICLE WAS CONTACTED. THE PARTS DEPARTMENT WAS NOT AWARE OF ANY MANDATORY OR VOLUNTARY RECALLS OR SERVICE BULLETINS. HOWEVER, THEY KNEW THAT THE HEADLAMP SWITCH WAS UPGRADED WITH A SOLID STATE DIMMER COMPONENT (P/N 56021889-AA).