What was found
FLYING LOW THRU MOUNTAIN PASS, TRIED TO TURN ON INSTRUMENT LIGHTS. MUCH SMOKE IN CABIN, TURNED OFF MASTER. FOUND RESISTOR WINDINGS FAILED, CONTACT ARM BURNED THRU TO CASE, ALSO CIRCUT BREAKER DID NOT OPEN. FOUND PLASTIC TRIM PANEL HOLE HAD EGG SHAPE, BUTTON COULD NOT POP OUT. REMOVE BACK OF SWITCH AND INSPECT. BETTER TO REPLACE WITH PUSH-PULL SWITCH AND CHECK CIRCUIT BREAKERS.