I have a 1987 F150 and it's been in my possession for less than 2 weeks. I'm still learning the ins and outs, and have bought Chilton and Haynes repair manuals. But while vacuuming the carpet, I saw behind the bench seat a cable that puzzled me. I flipped through the books and couldn't find anything, but I really don't know what I'm looking for (I'm not mechanically inclined whatsoever, but I'm trying to learn). Included are 2 pictures, one picture of the cables hooked and one picture of them unhooked. One side comes through the middle seatbelt area, and the other is on the back wall area. I haven't a clue as to what it hooks up to and does.. Please forgive my ignorance and help me figure it out

 

likely the sensor cable for the seat belt light on the dash..

 

Seatbelt plug for the buzzer/light. It could be for power lumbar if you have that; they look the same.
Anyway it's not supposed to be plugged in that way; drop the seat end back down through the seatbelt hole and plug it in under the seat. The way it is the wires could get rubbed bare and cause a short.