Where is the inertia switch on a 1983 Oldsmobile Cutlass Ciera?

Inertia switch? If you're referring to the seat belt mechanism, all the components are low on the B-pillar. If the inertia mechanism sticks, it can usually be reset by opening the door, allowing a small plastic button to pop out at the lower-rear corner of the door. If it becomes too much of a hassle, you may want to look into lubricating it, but not before reviewing a service manual to see the applicable safety measures.