What was found
WHEN PERFORMING BUSS SENSE TEST, LOW VOLTAGE (11V-18V) WAS STILL PRESENT ON CENTER BUSS WITH BUSS TIE RELAYS OPEN. IT WAS DETERMINED SOURCE OF VOLTAGE WAS RT GENERATOR BUSS. WHILE SYSTEMATICALLY OPENING CB POWERED OFF RT GENERATOR BUS, VOLTAGE ON CENTER BUSS DISAPPEARED WHEN THE ELEVATOR TRIM CB WAS PULLED. HOWEVER IT WAS DETERMINED THAT THE ELEVATOR TRIM MOTOR WOULD STILL RUN WHEN COMMANDED EVEN WITH ITS CB OPEN IF THE NAV LIGHTS WERE SELECTED ON. THE SHORT BETWEEN THE NAV LIGHT CIRCUIT (CENTER BUSS POWER) AND THE ELEVATOR TRIM CIRCUIT (RT GENERATOR BUS POWER) OCCURRED IN THE AFT PRESSURE BULKHEAD FEED THROUGH CONNECTOR. REPLACED FEED THROUGH FT393 AND PINS 2 AND 5 IN MATING PLUG P394.