It is attached to the liftgate latch assembly.
Check the plunger switch in the door. Sounds like it is shorted closed.
Check your guage light dimmer wheel ( just to the right of your headlight switch ) to see if it has been rotated all the way up - that turns on your interior lights. Also , if you are getting a door ajar warning light in your gauge cluster you could have a door ajar switch sticking inside one of your doors , liftgate , or for the liftgate glass
The door ajar switch on the 2008 Ford Sport is located inside the door that is mounted on the backside.
Just to the right of your headlight switch is a dimmer wheel for your gauge lighting If the dimmer wheel has been rotated all the way up , your interior courtesy lights will stay on ( even with your doors closed ) If your interior lights are on with a door ajar indicator light on in your gauge cluster , either a door ,your liftgate , or your liftgate glass is not closed or you have a sticking door ajar switch (Helpfull)
If the door ajar light is coming on in your gauge cluster, and the warning chime is sounding when all your doors, liftgate, and glass hatch are securely shut you most likely have a sticking door ajar switch. The door ajar switches are inside the doors mounted on the latch mechanisms.
I'm not a mechanic / technician but on a 1997 Ford Explorer I believe that if the gauge panel dimmer switch ( to the right of your headlight switch ) is rotated all the way up it will turn on all the interior courtesy lights when the doors are closed Also , is the " DOOR AJAR " warning light on in your dash to the left of the fuel gauge , if so either a door or the liftgate is slightly ajar or a door ajar switch is sticking , I believe that will also keep the interior lights on
On my 1995 Ford Explorer , to lower the underbody spare tire , I open the liftgate and the access hole is located above the rear bumper at the center of the bumper ( I assume your Ford Aerostar would be similar )
If they say on, that mans you have a door or rear lathcing liftgate/door that is ajar...make sure ALL doors al completely closed...if they are...you maight have a door switch that is faulty.
Huh?
ask a technition
On the 1989 Aerostar it is under the dash near the passenger door.
I have a 1995 Aerostar and the switch is on the passenger side, inside the door, down below the dash, behind the moulding. Hopes that this helps.