DOH! I feel stupid, I missed where he said that.

Stumpy is correct, No electricity to a mechanical guage.

Disconnect the guage from the tube and start the car for a few seconds. Oil should come out of the tube. If not you got problems, could be a bad tube but more than likely a bad oil pump drive since the problem just popped up.

If oil comes out then try a new guage you trust. If the pressure is still low/none then check the oil pump drive for rounding off.