What was found
THE FLIGHT CREW REPORTED THAT THE ENGINES WOULD ONLY START WHILE ON EXTERNAL POWER. THE MAINTENANCE TROUBLESHOT AND FOUND THAT THE GROUND POWER SUPPLY CABLE FOR THE GROUND CONTACTOR RELAY WAS CHAFING AND ARCING ON AN ADJACENT BUSS-BAR STRAP. BOTH THE CABLE AND STRAP WERE DAMAGED ALONG WITH THE GROUND CONTACTOR. ALL THREE ITEMS WERE REPLACED WITH NEW AND THE CABLE WAS REPOSITIONED TO PREVENT FURTHER DAMAGE. OPS CHECKS WERE SATISFACTORY. THE AIRCRAFT WAS RETURNED TO SERVICE