What was found
ON CLIMB-OUT, "FIRE DETECT 2 FAIL" WHICH GAVE US NOT DETECTION CAPABILITY ON ENG NR 2. AIR-TURN-BACK TO LAX, EXTINGUISHED ON TURN BACK TO LAX. FOUND WIRES CHAFING ON LEFT T/R LOOP. SPLICED LEFT LOOP A AND B WIRES. LOOP A CHECKS NORMAL, FDCU FAULTS LOOP B LEFT SIDE. REMOVED LT A/B LOOP HARNESS FROM RESPONDERS AND FOUND THAT EVEN WITH THE NEW SPLICES, THE HARNESS SHOWED SHORT TO SHIELD/GROUND ON BOTH A/B. DECIDED TO REMOVE AND REPLACE ENTIRE HARNESS. REMOVED OLD HARNESS. PARTIALLY INSTALLED NEW HARNESS. INSTALLED NEW LT FIRE LOOP HARNESS. PERFORMED FIRE DETECTION BITE TEST. ALL TESTS PASSED.