avital 5103 in 97 mountaineer

I've gotten everything to work but one little thing, and it's driving me crazy. I'm installing an Avital 5103 into a 97 Mounty with NO PATS. With the factory fob, if I'm outside the truck with all doors closed and press the factory lock button, the "theft" light comes on and the factory anti-theft is activated. If I'm outside the truck with the Avital remote and all doors closed, and press the Avital lock button, the doors lock, the Avital arms, but no factory anti-theft. So here's the strange part. If I leave the driver's door open, press the Avital lock on the fob, it locks the doors, sets the Avital AND the factory anti-theft. I want the factory anti-theft to set with all doors closed as well, but I can't find any listing for a factory arm wire to tap. Anyone with experience who could point me in the right direction??

According to Ready Remote, the vehicle will only arm when you lock and the door is opened. so just pulse the door pin while locking and it should arm the alarm.