oil pressure gauge

Howdy - still trying to track down what's faulty - the gauge or the sensor unit. Tried to measure resistance (ohms) across the two leads out of the oil pressure send unit and got nothing, not while the motor was running nor while it was off. Does anyone know offhand if there should be resistance and how much?

Is there a site/post somewhere that I've missed that can tell me the various resistances, etc of the various parts of the electrical system? I've got three manuals that don't seem to go into detail on this (haynes, clymer & clifton (?))

I've a '78 280z 2+2

Any help would be great!

Cheers!