What was found
RED CARGO DOOR LIGHT ILLUMINATED IN FLIGHT AT FL330. QRH CONSULTED, PRESSURIZATION OPERATED NORMAL. INSPECTED MCD WARNING SYSTEM, NO FAULTS FOUND. ADJUSTED FWD VENT DOOR SWITCH S-AE9, LUBED MCD SYSTEM OPS CHECKED NORMAL IAW AMM 52-33-01 AND WDS 52-35-12. AIRCRAFT GROUNDED.