What was found
KMIA - FLT 78614 - NR 2 ENGINE A-LOOP LIGHT CAME ON WHILE SETTING CLIMB THRUST AFTER TAKEOFF. SELECTED LOOP B AND TESTED OK. WENT BACK TO BOTH POSITIONS AND A AND B LOOPS WERE ON WITH LIGHTS AND BELL. RAN ENGINE FIRE AND SEVERE DAMAGE CHECKLIST ALONG WITH LOSS OF BLEED AND ONE GENERATOR CHECKLIST. WHEN FIREWALL SHUT OFF HANDLE WAS PULLED, A AND B LIGHTS WENT OUT, AND RED FIRE LIGHTS WENT OUT. RETESTED FIRE WARNING, ALL OK. ELECTED NOT TO DISCHARGE BOTTLE. REMOVED AND REPLACED NR 2 ENGINE FIRE DETECTION CONTROL UNIT IAW L1011 MM 26-11-08 AND HORIZONTAL FIREWALL FIRE DETECTION SENSOR IAW L1011 MM 26-11-03. INSPECTED ALL OTHER FIRE DETECTION SENSORS IAW L1011 MM 26-11-00. NO DEFECTS NOTED. INSPECTED ALL