What was found
(CAN) DURING ROUTINE MAINTENANCE, CABIN BEGAN TO FILL WITH SMOKE. A/C POWER WAS DISCONNECTED & A SEARCH WAS CONDUCTED TO LOCATE THE SOURCE. IT WAS FOUND THAT THE PASSENGER COMPARTMENTENTRANCE LIGHTING SYSTEM WAS AT FAULT. WIRE HARNESS W185 HAD CHAFFED ON THE AIRCRAFT STRUCTURE IN T HE CABIN DOOR UNDER FLOOR AREA AND SHORTED TO GROUND. THE INSULATION ON WIRES HAD MELTED AWAY CAUSING THE SMOKE IN THE CABIN. AN INSPECTION OF THE ENTIRE WIRE BUNDLE FROM HOT BATTERY BUSS IN THE RIGHT WING ROOT THROUGH THE AIRCRAFT FUSELAGE TO THE CABIN DOOR AREA REVEALED SEVERAL SCORCHED WIRES. THESE WIRES WERE REPAIRED AS NECESSARY.