As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE GND POWER WAS CONNECTED POWER DROPPED OFF & THERE WAS ARCHING AT EXTERNAL POWER RECEPTACLE DUE TO GND POWER. GND POWER PUT ON MEL, REPLACED EXTERNAL POWER RECEPTACLE IAW MM24-41-11-400-801, CHECKED GOOD. REPLACED EXTERNAL POWER BUS CONTROL UNIT IAW MM24-41-21-400-801, TESTED GOOD. ROTABLE PARTS CHANGE WAS INDICATED TT 1600484 SN OFF 01020 UNIT, BUS POWER OFF 29-2441-9-0005 1020 & ON 29-2441-9-0005 4832.