What was found
WHILE IN HEAVY CHECK: WHEN EMERGENCY LIGHT TEST BUTTON IS PRESSED ON FWD OR AFT FAP THE FOLLOWING LIGHTS DO NOT ILLUMINATE: AFT RH PASSAGEWAY SIGN, AFT RH EXIT MARKING SIGN, AFT RH EXIT IDENTIFIER SIGN, CABIN EMERGENCY-LIGHT ABOVE SEAT ROW 12 AND 20, BUT WILL ILLUMINATE WHEN EMERGENCY LIGHTS ARE SWITCHED ON FROM COCKPIT, OR EITHER FAP. : REMOVED PAX CABIN CEILING PANEL 254CRC, REMOVED EMERGENCY-LIGHT POWER- UNIT BATTERY #4, P/N: 3400-22-10, S/N: 002601, AND REPLACED WITH P/N: 3400-22-10, S/N 001500. REINSTALLED PAX CEILING PANEL 254CRC. PERFORMED OPS CHECK, OPS CHECK GOOD. REF AMM 33-50-01, 25-22-07, AND 33-50-00