As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOW VOLTAGE LIGHT ILLUMINATED IN-FLIGHT. INSPECTION REVEALED NO VOLTAGE TO FIELD TERMINAL ON ALTERNATOR. VERIFIED POWER SUPPLY TO ACU. NO ACU OUTPUT. INSTALLATION OF TWO ACU'S (ZERO TIME SINCE REPAIR/OVERHAUL) DID NOT RESTORE POWER. INSTALLATION OF ZEFTRONICS ACU P/N R25400 RESTORED POWER AND SYSTEM FUNCTIONED NORMALLY.