With issues like the door ajar, the problem is almost always a sticky switch in the latch. The first thing you need to do is get a wiring diagram for your year and model. Then you can use a multimeter to figure out which switch on which door is giving you the issue.
Once this is done you can flood the latch with lots of WD40 but i recommend taking the door panel off so you can get at more of the assembly. Spray it liberally into every crack and cranny you can find in the assembly. After flooding it good you will need to vigorously work the door assembly to work the WD into the parts. After a short stint of opening and closing the door hopefully it will start working properly.
If you are able to get it working properly with just the WD then I would recommend cleaning out the WD with contact cleaner and using a spray in dry lubricant. WD will collect dust and dirt over time and your problem will return.
If you are unable to get it working verify the switch operation with a multimeter inside the door by carefully pushing the multimeter leads into the wire insulation. If you have verified that the switch is truly still not working properly then you need to make a trip to get a new latch assembly.
The whole key is in isolating the problematic door latch. If they all test good then you can start looking for wiring or module issues.
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1998 EB Expedition 4X4 200,000+, 1999 Windstar 200,000+ (Needs Head Gasket), 2008 Chev Colorado (Company Truck, Really sucks but it's free)
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