If your door ajar light is on, try lubricating all of your door latches with WD40, this is a common problem on the Ford Super Duty's. Lube the latches and open and close the doors several times and loosen the latch up. It is usually the quickest and easiest fix. Good luck. If your locks arent working, just maybe, the lock actuators are shot. Both of mine on my truck went out at the same time, replaced them, and everything works great now.