What was found
PHL - FLT 1845 - AFTER TAKEOFF PHL/MIA - ALL 3 RED GEAR WARNING LIGHTS AND TAIL SKID LIGHT ILLUMINATED WITH GEAR HANDLE IN UP POSITION. AIRCRAFT RETURNED TO PHL AND LANDED WITHOUT INCIDENT. AIRCRAFT FERRIED TO LGA. REPLACED LANDING GEAR HANDLE DOWN SWITCH. ALSO, REPLACED LEFT MAIN LANDING GEAR DOWNLOCK PROXIMITY SENSOR. ACCOMPLISHED GEAR RETRACTION CHECK. SYSTEM GROUND CHECKED, NORMAL OPERATION. (X)