What was found
SHIELDED WIRE FROM INSTRUMENT PANEL TO AFT OF BAGGAGE COMPARTMENT UNDER FLOOR WAS NOT CONNECTED TO ANYTHING. SHIELDING WAS GROUNDED AT INSTRUMENT PANEL. WIRE WAS LOOSE IN AREA OF BATTERY BOX AND MASTER SWITCH. IN-FLIGHT, WIRE APPARENTLY TOUCHED AGAINST THE TERMINAL ON THE MASTER SWITCH CAUSING A DIRECT SHORT TO GROUND BURNING THE INSULATION ON THE WIRE INSIDE THE SHIELDING CAUSING SMOKE IN THE COCKPIT. RECOMMEND ANYTIME ELECTRICAL WIRES ARE DISCONNECTED, THEY BE REMOVED FROM THE AIRCRAFT.