As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHEN SWITCHING FROM GROUND POWER TO APU POWER, THE RIGHT SOURCE OFF LIGHT ILLUMINATED. ACFT GROUNDED. WHILE EVALUATING VERIFIED FAULT. REPLACED BPCU & APU GCU WITH SERVICEABLE PARTS. ACCOMPLISHED INSTALLATION TEST OF BOTH THE BPCU & APU GCU. BOTH PASSED. ACCOMPLISHED EVALUATION AND NOW NO FAULTS. IAW FIM 24-21 TASK 823, AMM 24-41-21-400-801, AND AMM 24-21-81-400-801.