1999 F250 Super Duty XL; Door Adjar light stays on sometimes as well as the interior light, can't find reason nor how the system and or the switch works or even where it is. A little HELP?

 

There have been many recent post on this. You need to get some PB Blaster rust penetrant and thoroughly douse the door latches on both driver and passenger sides. Concentrate your efforts toward the bottom of the latch as this is where the door ajar switch is located and gets stuck. After spraying work the door open and shut a bunch of times and spray more penetrant. After working door latched and unlatched about 50 times see if problem goes away and then sparay with some sort of white lithium grease, and this ought to take care of problem.