Oil pressure sending unit replacement

On a 1984 there is no ECM input from that sensor. There should only be two types of sender for that year, one works with a gauge while the other is just a switch. They are not interchangeable. The two types are shown in the images attached. If you have the switch type and the light is staying on, look at the wiring to be sure it is not grounded as that is how those work, the switch is pushed off as the oil pressure rises past the trip point of about 5-10 PSI depending on the actual switch design. For the gauge style the resistance changes as the pressure changes so if the gauge isn't working, again check the wiring at the connector. In both cases corrosion or damage will stop them from operating.