What was found
AT 10,000 FT MSL MASTER FIRE WARNING SOUNDED MOMENTARILY NR 2 FIRE HANDLE ILLUMINATED, APPROX 30 SECONDS LATER MASTER FIRE WARNING SOUNDED MOMENTARILY AGAIN AND NR 3 FIRE HANDLE ILLUMINATED. ENGINE SEVERE DAMAGE OR SEPARATION CHECKLIST INITIATED, ENGINE NR 1, 2, 3 FIRE WARNING TESTED OK AND NR 4 DID NOT. ON THE SECOND IDENTIFY ENGINE NR 1, 2, 4 TESTED OK AND NR 3 DID NOT. AIRCRAFT RETURNED TO MIAMI WITHOUT INCIDENT. OVERWEIGHT LANDING PERFORMED INTO MIAMI. PERFORMED NR 2 ENGINE ELECTRICAL WIRING CHECK, FOUND NORMAL, FOR T/S REMOVED AND REPLACED NR 2 AMPLIFIER FIRE WARNING IAW MM 26-10-4 (WD 26-1-1). PERFORMED NR 3 ENGINE ELECTRICAL WIRING CHECK FOUND NORMAL IAW WD 26-1-1, FOR T/S REM.