Where is the door switch that controls Door Ajar light and also interior lights on a 98 Ford Ranger?

The door ajar switch on a 1998 Ford Ranger is located in the door jamb itself, not on the door itself. There's usually one switch per door. It's a small, often rectangular switch embedded in the rubber boot that surrounds the door jamb. It's easily overlooked because it's a small part tucked into a not-so-obvious place.

To find it, carefully inspect the rubber boot where the door frame meets the car body. You might need to gently squeeze the boot or move it aside to see the switch. It's usually on the driver's side (left) door jamb, but there may be similar switches on other doors as well, contributing to the overall "door ajar" signal. If the light stays on, there might be a problem with one (or more) of these switches, their wiring, or even a faulty control module.