Am actually having the same issues with mine too. The FSM has a wiring diagram in the VTSS sections. On my 97 if you access the BCM under the dash you can then use the diagrams to test the pins on the BCM and figure out which sensors are not what they should be. My project today.
By the way on mine the Door Ajar switch for the hatch is a microswitch in the hatch latch itself.
UPDATE: SAVE SOME TROUBLE, JUST DISCONNECT THE SWITCH AND SEE IF THE VTSS GOES BACK TO NORMAL. You can just cut one of the wires. Close the other doors and see if the alarm sets. IF SO, THE SWITCH IS BAD. My lesson learned after ripping apart the dash it led me to the rear door ajar, disconnected it and the signal went from +12 to 0vdc. SO the switch is open in the 'door ajar' position, just like all the other doors. Just disconnect it and it thinks the door is shut.
That being said, if the rear hatch is closed but not closed all the way, (you have to really slam it) it will also indicate open. SEE below post.