What was found
ON TAKEOFF, THE LANDING GEAR WARNING HORN CAME ON (UNTIL IT WAS RAISED). WHEN GEAR HANDLE WAS RAISED, THE RED LIGHT STAYED ON AND THE GEAR DOOR LIGHT WENT OUT. CYCLED THE LANDING GEAR AND GOT 3 DOWN AND LOCKED (NORMAL INDICATIONS). WHEN GEAR WAS RAISED AGAIN, THE RED WARNING LIGHT REMAINED LIT. REPLACED SWITCH S-320, SYSTEM CKS NORMAL PER M/M.