1998 Ford Ranger Door/Ajar Light?

[Greatman1]

Hello, I bought a used Ford Ranger and have no problems until I realized that the Door/Ajar light would stay on causing the light to stay on in my truck and not letting me listen to radio with the keys in the ignition. It stays on as if the door is open when I know I closed them well. Do you guys know what might be causing the problem? and how much to fix it?...the other day I noticed it turned off just for one day but the never again..any ideas would be appreciated