1997 Ford F-150

The door ajar warning light and interior light stays on for sometimes up to 1 hr after shuting the door. What is the problem?
The funny thing about it is, it only happen after the truck is warmed up, never in the early morning.

Very simple. You need a door latch switch. It is dirty and sticking. You may be able to shortcut replacing it by sprayind some wd40 inside the latch on the door liberally and open and shut door a couple of times.