What was found
AFTER TAKEOFF FROM LT MAIN GEAR UNSAFE (RED) LIGHT STAYED ON AND STARTED FLASHING. GEAR HANDLE UNSAFE LIGHT ILLUMINATED THE SAME AS THE GEAR HANDLE AMNUNCIATOR LIGHT. RETURNED TO FIELD. LANDING UNEVENTFUL. REMOVED LT MLG PROXIMITY SENSORS IAW AMM 32-61-06-000-802. INSTALLED NEW FROM STOCK LT MLG BOTH PROXIMITY SENSORS. IAW AMM TASK 32-61-06-400-802 PARA 1-4A. STEPS (1)J AND (8) THRU (16). STEPS (2) THRU (7) NOT REQUIRED HARNESS ALREADY MADE UP. PARA 5 A.B.C., PARA D NOT REQUIRED ONLY DOWN LOCKS REPLACED. RETURNED TO SERVICE.