What was found
DURING SCHEDULED OVERNIGHT MAINTENANCE, APU RUNNING & GROUND POWER HOOKED UP, CLEANING CREW & MX SMELLED SMOKE THEN COCKPIT BEGAN TO FILL WITH BLACK SMOKE. ACFT EVACUATED & GROUND POWER DISCONNECTED. EXTERNAL POWER RECEPTACLE DETERMINED TO BE CULPRIT, BURNED PIN ON EXTERNAL POWER RECEPTACLE WITH WIRE COVER BURNED 6 INCHES BACK FROM PIN FOUND. ACFT INSPECTED FOR A MAINTENANCE FERRY BACK TO PHX FOR FURTHER REPAIR. EXTERNAL POWER RECEPTACLE REPLACED AND SEVERAL WIRES REPLACED IAW AIRBUS 320 AMM 20-48-11, WDM DRAWING 24-41-01 AND EPSM 20-43-11, 20-42-11, AND 20-48-11. OPS CHECKS GOOD IAW AIRBUS 329 AMM 24-41-52. GPU & PLUG WERE FOUND TO BE WITHIN LIMITS, PLUG REPLACED DUE TO WEAR AND BARE METAL EXPOSED.