What was found
FLT 42, ENG NR 1 (OVERHEAT WARN) LIGHT FLICKERING DURING TAXI. RETURNED TO BLOCK. TRIED FIRE CONTROL MODULE, FIRE DETECTION UNIT AND DISCONNECTED NR1 ENG FIREWALL CONNECTOR, LIGHT STILL FLICKERING. RE-INSTALLED ORIGINAL COMPONENTS AND CONNECTOR. REMOVED AND REPLACED THE NR 1 ENGINE LWR FIRE WARN LOOP IAW MM26-11-11. OPS CK GOOD ON GROUND. REMOVED AND REPLACED ENG/APU FIRE DETECTION CONTROL UNIT IN THE EE BAY. OPS CHECKED GOOD ON GROUND. ACFT RETURNED TO SERVICE.