I have a 1989 Toyota Camry and am having difficulty with driver seat belt activation. What sensor or component tells the seatbelt to activate? Where is it located?

I have a 1990 camry and my driver side belt stopped working too. The problem is the wires that run from the door to inside the vehicle. Open your door, look in the doorjam for the black rubber piece. The wires inside it bend every time you open and close your door and eventually break. The only solution is to cut the rubber and resplice the wires which is a big pain in the ***. It took me a few frustrating hours, but, I heard it's easier if you take the door off. I left a lengthy amount of wire, wrapped in electrical tape, behind the front quarter panel to prevent it from bending again. This is a very common problem with camrys of these years.