warning signal continues to sound after doors are closed and key is removed. Why

Crummy design. The door jamb switch that used to be located by your toe on the "A" pillar was relocated to the bottom of the door latch inside the door panel by some genius at Ford. Since it is positioned upside down, it collects dirt, water and dirt collecting lubricants from well-meaning, uneducated Lube shops. You'll need to pull the door panel. You can reach the switch but it's a mother-@#$ to replace without loosening or removing the door latch, linkages and wires. It's on the very bottom of the latch and almost right up against the inside of the door. A quarter turn counter-clockwise will remove it. The biggest bummer is that there's almost no way of telling which door it is without at least pulling the panel and unplugging the switch. Go slow and be careful, I've done a million of them (ok, more like 2 dozen) and almost always tear up my arms.

Yep, Tracy's got it right. My best guess is that it will be the drivers side door. I've done a couple and it is always that side. Probably because it is the door used most often. And since my hands are large and my forearm larger than most, I always have to remove the lock. It is a #$%^&*

Tracey. I am contemplating a retrofit the next time I have to fix one of those. It has to be a momentary switch, but is it normally off or normally on.

It looks like a Normally Closed, un-grounded circuit. 3 wires.

Mine is a 1994 ford Lightning were is this switch located