I am trying to answer a question that I saw earlier and have been unable to locate the question again. Door locks not working, radio does not stay on when key is turned off, dome light goes out quickly, door ajar light stays on, security light not flashing when doors are locked, etc. I had all of these problems and took mine to a dealership and had them replace the VEHICLE SECURITY MODULE. This must be done at a dealership because they have to download the information and upload to the new module. Bad news is that it was around $500. I will be happy to answer any questions regarding this. Hope this helps everybody else having the same problems.

 

I had some of those same problems with my 02 crew cab. Some times the door ajar light would stay on, sometimes not. When it stay'd on the doors would not lock, if I locked them from inside they'd unlock. Interior lights stay'd on until they timed out. I removed the d.s. front door panel. Pretty simple really, Two screws, one behind the light on the door panel (bezel just pops off from the back) and the other one is under the electric windows/locks panel. It just snaps out also. Remove those two screws and lift up on the panel and it comes off.
You DON"T need to remove the panel, I just put that in for your information if you need to get in there. I found that the door hatch in the door must not have been working completely. After I found that there were wires going to the latch and not the hinges, I had the door open and used a screw driver to operate the door latch (simulate closing the door). Everything worked as it is suppose to. Then I opened the outside door handle and slid the screwdriver out (this opened the hatching mechanism). The door chim came on. I did this a half dozen times. Each time I simulated a door close (again screw driver triping the latch into the closed position) the chimes went off. Opening the outside handle and sliding the screwdriver out (opening the latch) caused the chims to come on again. Now every time I open and close the door the system works like it was designed. One thing be sure to have the latch in the open position before closing the door for real. If the driver's door doesn't correct the problem try the other doors. It worked for me. Good luck

 

Here is some interesting related reading for those with 2002 model trucks.
https://www.ford-trucks.com/forums/4...ght=VSM+theory

 

Same problem w/ the door ajar. Turned out to be the instrument cluster. $700 at the dealer because they have to input the milage. Next time it comes on I'm going to cut the leads to the switch and wire nut em' together.