What was found
INCOMING DISCREPANCY STATED 'CANNOT APPLY EXTERNAL POWER TO AIRCRAFT.' DROPS OFF-LINE IN SEVERAL SECONDS. TROUBLESHOOTING REVEALED THAT THE GROUND STUD OF THE GROUND POWER RECEPTABLE WAS 'OPEN' TO AIRCRAFT STRUCTURE. FURTHER INVESTIGATION REVEALED THE NUTPLATE AND STRUCTURE WERE DESTROYED AT THE POINT WHERE THE GROUND WIRE ATTACHES TO THE AIRFRAME. AT FRAME 39. THIS POINT IS LOCATED BELOW THE BATTERY BOX FLOOR, APPROXIMATELY 1 INCH BELOW THE APU FUEL FEED LINE. THE COMPARTMENT IS SEALED STRUCTURE AND ALSO CONTAINS THE APU SHUT-OFF VALVE AND APU. FUEL BOOST PUMP AREA WAS REPAIRED IAW FALCON 20 MRI CHAPTER 51-30-03 AND FALCON JET ENG RECOMMENDATIONS. REPLACED TERMINAL P/N 324045 INSTALLING NEW UNIT.