What was found
WHILE UNDERGOING A C CHECK HEAVY MX VISIT, IN THE HANGAR A FIRE STARTED IN THE CTR ACCESSORY COMPARTMENT OF THE ACFT. TROUBLESHOOTING WAS UNDERWAY FOR THE FOLLOWING FINDING, CAC, BATTERY CHARGER BATTERY FAULT T SENSE B. A PUSHED BACK PIN HAD BEEN FOUND & CORRECTED IN A PLUG IN THE OVERHEAT DETECTION SYS & IT WAS TIME TO VERIFY IF IT WAS A GOOD FIX. THE MAIN BATTERIES WERE REINSTALLED & RECONNECTED. THE INSTANT THE BATTERY SWITCH IN THE COCKPIT WAS PLACED IN, THE ON POSITION THE GROUNDING CABLE ADJACENT THE B BATTERY OVERHEATED & THE WIRE INSULATION CAUGHT FIRE. THE BATTERY POWER SWITCH WAS IMMEDIATELY SWITCHED TO THE OFF POSITION & EXTERNAL POWER WAS REMOVED FROM THE ACFT. A TYPE B C PORTABLE FIRE EXTINGUISHER WAS USED TO EXTINGUISH THE FIRE. THE EXTINGUISHING AGENT WAS VACUUMED UP SO THAT ANY STRUCTURE THAT MAY HAVE BEEN EXPOSED TO A HEAT SOURCE CAN BE INSPECTED IAW THE SRM. NON-ROUTINES TO REPLACE THE WIRES HAVE BEEN GENERATED. THE MAIN BATTERY IS SUSPECT & HAS BEEN REMOVED FOR REPLACEMENT.