What was found
#1 ENGINE FIRE SWITCH NOT LIGHTING UP CORRECTLY DURING OVERHEAT/FIRE TEST. GROUNDED - YES. PERFORMED ALTERNATE DEACTIVATION REF CHAP 5 TABLE 3 ITEM 7. COULD NOT DUPLICATE DEFECT, OVERHEAT/FIRE TEST OPERATES NORMALLY. TESTED ALL 4 A LOOP DETECTORS, ALL 4 DETECTORS WITHIN LIMITS REF B737-800 WDM 26-11-11-1. INSPECTED ALL A LOOP HARNESS TERMINAL LUGS, NO DEFECTS FOUND. DUE TO HISTORY, REMOVED AND REPLACED ENGINE AND APU FIRE/OVERHEAT DETECTION CONTROL MODULE REF B737-800 AMM 26-10-01/401. OP CHECK GOOD. THIS CLEARS MEL 26-2B CN 20058560, PLACARDS REMOVED. REVERSED ALTERNATE DEACTIVATION PROCEDURES.