It is a small silver can with several electrical contacts on the end. It is on the right hand side of the engine block, way down near the edge of the oil pan. The sender itself might be bad, or the wiring harness connector could have bad mating contacts, or broken wires. The place it sits ensures that it gets lots of abuse from road debris over the years, and that connector is often damaged. The original oil pressure senders also have a reputation for failing early, and cheap aftermarket senders are often not much better. One of our forum members, Z Man of Washington, sells an aftermarket replacement that is more expensive, but is of a better design.