As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
#2 SOURCE OFF LIGHT ILLUMINATED WHEN APU GEN PUT ON BUS. DID NOT CLEAR UNTIL APU REMOVED FROM BOTH GEN BUSSES AND RECONNECTED. GROUNDED - YES. PERFORMED FIM SOURCE OFF LIGHT ILLUMINATES WITH GRD POWER AVAILABLE TO ON POSITION AND APU OPERATING VERIFIED SOURCE OFF LIGHTS OPERATES NORMAL WHEN APPLIED POWER FROM APU GENERATOR AS PER FIM 24-21 TASK 823.