The door ajar switches are near the door locks. They turn on the door-ajar light in the instrument cluster, activate their respective motorized seatbelts via the Passive Restraint Module, and signal the factory anti-theft module.
The door courtesy lamp switches are near the door hinges. The passenger-side switch turns on the courtesy lamps. The driver side switch is a double switch, with one switch turning on the courtesy lamps and the other switch triggering the Passive Restraint Module and the Warning Chime Module.
NateM, one half of your driver-side courtesy lamp switch might be bad.
tadrian2, you might have a bad door ajar switch on either side, which would also cause trouble for the motorized seatbelts in a non-Canadian car.