As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WITH AIRCRAFT ON GROUND WITH APU RUNNING, THE ESSENTIAL AND MAIN BUSS VOLTAGES DROPPED TO 19VDC. TROUBLESHOT SYSTEM AND FOUND THAT THE REVERSE CURRENT RELAY A700AH SN L13232 DID NOT PROPERLY SERVE AS A REVERSE CURRENT RELAY AND IT FED POWER TO THE DC GENERATOR RELAY. THIS RELAY HAD 1 HOUR AND 3 CYCLES SINCE INSTALLATION AS AN OVERHAULED PART.