As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER SWITCHING FROM APU TO GROUND POWER, POWER DROPPED OFF WITH ELECTRICAL BURNING ODOR IN E/E BAY AND FLIGHT DECK. FOUND AT P300 AUX PANEL, SOURCE OF BURNED ODOR. CONTACT RELAY ON PANEL WAS BURNED. REMOVED CONTACT C24335 AND FOUND D432 DAMAGED AND RELAY C24004 DAMAGED.