The above will work, then get your Clifford alarm installed correctly, if it has sensed a door having been open since disarming it should not autolock, and is part of the thatcham criteria that it does not autolock after disarmiing where a door has been opened, or did you have it in position 2 ?
If you did not have it in position 2 but 1, the most likely cause is the door pin switch did not register the door opened, I replaced all four of mine with new as they corrode up, and mine did the same but I had a window open, I always leave one open when working on the car.
tabetha