What's the problem with 2002 Ford Ranger?

2002 Ford Ranger XLT v6
I Close doors securely and start driving. After a few minutes the "door ajar' alarm starts going off but the door ajar light on the board doesn't light up. It does work because if I open the door, it lights up. I try closing the door again and make sure cap on gas tank is closed but door ajar alarm still goes off. It runs for a few mminutes while I'm driving. What's the problem here?

The door ajar switches on Ford vehicles are a known problem. First clean them and see if the problem goes away. If it doesn't and you're still convinced the switches are good, then the problem is in the GEM module.

http://ricksfreeautorepairadvice.com/ford-door-switches/