What was found
LAS - AIR TURN BACK - FLT 0728 - AFTER TAKEOFF FROM LAS EN ROUTE FOR ORD IN GUSTY WIND CONDITIONS THE AFT CARGO DOOR LIGHT ILLUMINATED, TURNED BACK TO LAS AND LANDED WITHOUT FURTHER EVENT. MAINTENANCE INSPECTED AND CLEANED THE AFT CARGO DOOR LOCKING MECHANISM UNDER PANEL 826AR, CLEANED AFT CARGO DOOR PROXIMITY SENSOR AND TARGET, AND CHECKED SENSOR GAP, GAP WAS GOOD IAW AMM 52-32-00-501.