As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CABIN EMERGENCY LIGHTS COME ON WHEN EXTERNAL POWER IS REMOVED FROM ACFT. TROUBLESHOT ITEM TO AFT F/A PANEL. REPLACED AFT F/A PANEL, EMERGENCY LIGHTS FUNCTION GOOD. SWITCH POWER BACK AND FORTH FROM APU AND EXTERNAL POWER AND LIGHT FUNCTION WAS GOOD.