What was found
DURING FIRE DET TEST #1 ENG FIRE HANDLE AND OVHT LIGHT DO NOT ILLUMINATE. OKAY WITH B LOOP SELECTED. GROUNDED - YES. RELEASED PER ASA MEL 26-2B #1 ENG LOOP A FIRE DET INOP. LOOP B OPS CKS NORMAL. REMOVED & REPLACED LEFT CORE DET (M1759) REF B737-800 AMM 26-11-01-400-802. OPS CK GOOD REF AMM 26-11-00-710-801. THIS CLEARS MEL 26-2B. #1 FIRE LOOP TEST SWITCH RETURNED TO NORMAL POSITION. GROUND VERIFICATION SUCCESSFUL.