The oil pressure switch is only used on the 78 280Z and 280ZX's to control the fuel pump relay.  Look at the 1978 Engine Electrical chapter is you want to see how the pressure switch is used.  Your diagram is odd.  Looks like somebody created their own safety system.

The only wire that should be connected to the starter solenoid is the wire from the ignition switch.

I think I see what the diagram is trying to do.  But "ignition switch" doesn't tell if it's Run or Start.

I screwed up and misread the diagram.  Edit mode...

The problem is probably in the pressure switch.  The Nissan pressure switch passes current to ground.  Your diagram shows it as passing current to a pin on the switch.

http://www.texasindustrialelectric.com/relays_0332002155.asp

Edited June 13, 20213 yr by Zed Head

And, the switch is normally closed.  It opens when pressurized.

One last thing, in case you didn't know.  The oil pressure switch is actually a combination switch and sensor.  One pin supplies the pressure resistance for the gauge, the other pin supplies the ground signal to the fuel pump control relay.

If you're thinking that the "switch" is between the two pins, it's not.

I think that you could use this 5 pin relay to open when powered through the pressure switch but close when oil pressure is present (removing the ground path), supplying fuel pump power.  There would be a delay until oil pressure built up.  Might have to wire in a branch from the starter solenoid so that the pump gets power during Start.

You're probably done already but I felt like exercising (hurting) my brain a little bit more.  There is some neat stuff on that web site.

http://www.texasindustrialelectric.com/relays_0332209150.asp

Edited June 14, 20213 yr by Zed Head