What was found
PILOT REPORTED WHILE EN ROUTE FROM ONT TO SBA, THE RED GENERATOR OFF LIGHT ILLUMINATED. THE STAND-BY ALTERNATOR DID NOT COME ON LINE. THE STAND-BY ELECTRICAL POWER ON LIGHT NOR THE STAND-BY ELECTRICAL POWER OFF LIGHT ILLUMINATED. THE AIRCRAFT WAS OPERATING ON BATTERY POWER ONLY. THE PILOT ELECTED TO PERFORM A PRECAUTIONARY LANDING IN OXR. MAINTENANCE WAS DISPATCHED TO THE AIRCRAFT AND CONFIRMED A GCU FAILURE. THE GCU WAS REPLACED, ADJUSTED AND OPERATIONALLY CHECK GOOD. THE STAND-BY ALTERNATOR SYSTEM WAS FUNCTIONALLY CHECKED AND NO DISCREPANCIES WERE FOUND. THE AIRCRAFT WAS RETURNED TO SERVICE AND FLOWN TO FAT WITH NO DEVIATIONS.