I think I know the answer to this but can’t find a wiring diagram to verify it.

I have a TH 250 with lock up converter (84 El Camino) it has a 4 pin square plug on the transmission. Although there are 3 wires going to the plug on the harness, only 2 pins on the transmission plug are wired. I assume one pin is hot and the other is ground. Can anyone verify this or point me in the direction of a wiring diagram?