Where does the wire from the oil pressure switch that is located on a 1983 Nissan 720 pickup attach to?

Obviously, it attatches from oil pressure sender to both the controller, and, if equipped, the Oil Pressure Gauge.
The oil pressure switch is, ironically, one of the most leaky point on that engine.
It's located on the side of the engine block. There was a rubber boot designed to shield it, but that is probably gone by now.
I hope this can be of help.