What was found
(CAN) DURING TAXIING OUT FOR TAKEOFF, SMOKE AND FIRE OBSERVED COMING FROM OVERHEAD ELECTRICAL PANEL IN COCKPIT. EMERGENCY EVACUATION DRILL CARRIED OUT AND PORTABLE FIRE EXTINGUISHER DISCHARGED INTO FIRE AREA AND FIRE EXTINGUISHED. MAINTENANCE INVESTIGATION REVEALED WIRING BURNT IN VICINITY OF THE ENGINE IGNITION ELECTRICAL SWITCH WHICH HAD FAILED INTERNALLY. WIRING AND SWITCH REPLACED.