Oil pressure sender unit confusion

Got my newly rebuilt 360 back in my Lil Red, WOHOOO!!

The 1979 Lil Red Express truck has an original oil pressure gauge(no warning-light), but for some reason the previous owner had installed a non-electronic Bosch aftermarket oil pressure gauge, connected with a thin plastic tube.

I told the workshop to hook up the original gauge, so they installed an oil pressure sender that fitted the three terminal connector that was in place in the harness, but the gauge immediately pegged at 100 psi where the old showed 60 psi, something is wrong here, but what?

Picture of the connector that was in the truck and the new sender unit.IMG_6642.JPG Oil Pressure Sender Three terminals.jpg