As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOT REPORTED THAT ALL PILOT AND COPILOT INSTRUMENT LIGHTING WAS NOT WORKING ON THE GROUND PRIOR ENGINE START. AFTER INVESTIGATION WE FOUND THAT THE COPILOT AIRSPEED INDICATOR WIRE L38B20 HAVE BEEN CHAFFING ON EADI OUTERCASE. THE WIRE SHORTED AND CAUSED CIRCUIT BREAKER CB21 TO TRIP, CAUSING THE POWER LOST FOR THE INSTRUMENT LIGHTING.