Oil pressure sender unit confusion

Yes!

This was the type of sender that I had expected as well, still confused why the three terminal connector is there, I will look for a "hot" wire in the harness behind the engine.

Is this the the only type of sender for the oil pressure gauge, or are the several types to be aware of?
It's the only type I am aware of, and the only type I find listed for a '79 Little Red.