I completed this installation yesterday with an Autometer Phantom series Oil Pressure gauge w/ autometer's sender.
The install went good, however the gauge is not receiving a signal from the sender. After reading through install directions sent with gauge, I says to wire the ground from the gauge close to the sender unit (not sure why that is). I grounded my gauge to the 12v source that feeds my A-pillar setup. Also, if a remote kit is used, autometer reccomends to ground the sender from the body of sending unit.
Did OP ground his sending unit? Any thoughts or help is appreciated. My plan is to ground the oil pressure gauge to the battery directly. And solder a lead onto the sender body grounding that to engine compartment wall.