The interior lights on my 1998 ford expedition don't turn off when the doors are closed. the door ajar warning light goes on and off.

courtesy light switch , is door ajar switch an it's part of the door lock actuator . Light on coming on ? Not going off ? The ajar switch is a input to the GEM module , fords BCM - body control module . The GEM will energize a relay to turn on the lights .
The GEM will illuminate the interior lamps when any door is open or ajar. The interior lamps are; the dome lamp, the rear cargo lamp, the door courtesy lamp and the side rail lamps. The courtesy lamps will shut off when the doors are closed and the illuminated entry feature is not active or when the vehicle speed is greater than 5 mph (8 km/h). The interior lamps will not be reactivated until the vehicle speed is less than 3 mph (5 km/h) and a new door open warning lamp switch is received.
The GEM controls the interior lamps illuminated entry function by activating the interior lamp relay.
Mite be a good idea to have it check for DTC'S - diagnostic trouble codes .

B1322 Driver Door Ajar Circuit Short to Ground GEM GO to Pinpoint Test B . B1323 Door Ajar Lamp Circuit Failure GEM REFER to Section 413-01 . B1325 Door Ajar Lamp Circuit Short to Battery GEM REFER to Section 413-01 . B1330 Passenger Door Ajar Circuit Short to Ground GEM REFER to Section 417-02 . B1334 Decklid Ajar Rear Door Circuit Short to Ground GEM GO to Pinpoint Test C . B1338 Door Ajar RR Circuit Short to Ground

you have a bad door switch on one of the doors or liftgate. Look for push switch button where doors close on door opening. Open onedoor at a time and push button by hand and see if the lights go out. When you find the one that turns the light off, either adjust it, shim it or stick a cabinet door bumper on the soor so it psuhes the switch shut.

just spray the door latches with lubricant be sure the oil penetrates the internal machanism.

one of your door latch assembly is showing the door ajar,you will need to take it to Ford when it is raining and light is on for them to tell you which assembly is at fault

is the door ajar light on sometimes also when driving? I had a similar problem with the light staying on. I determined that it was the passenger front door latch sticking. I opened the door, then took a screwdriver to push the latch shut on the door jamb. (Make the truck think the door is shut even though it is open). Then lubricate that jamb and pull the handle open to open the door. Keep doing this (closing with screwdriver and opening with handle) until the latch works freely. This took care of my light and door ajar problem.

Spray some WD40 into the latches on the side of the doors then open and close the doors several times firmly.This will unstick the door adjar switch most of the time.Start with drivers door first.

the wire on the door latch make sure they are plugged in or unplug it and the light should go out if it does not then it's not that door

Try spraying WD-40 into the door latching mechanism (door side). I learned this fix after two battery replacements, but have only had to spray twice in the more than seven years of ownership

This is usually caused by the switches sticking in the door latches. Try spraying some WD40 in the latches and open and close the doors a bunch of times that should take care of it.

Our Ford Expedition & an Olds Silhouette Premier & both did the same thing. Someone online said to spray the inside door where the metal connects with the frame & sensors are there with WD-40. We did & it fixed the problem. Maybe this will work for yours.