My needle was constantly fluctuating and the gauge was in poor shape so I replaced that first w/ same Faria dress white gauge. When I turn the key to ign on the gauge pegs to the right same as old gauge but once started goes to about 50 at idle. When I rev the eng pressure drops. My ohms from disconnected terminal from back of gauge to ground w/ eng off is only about 2 ohms. I feel like as oil press increased so does the resitance and the gauge moves lower. I think I have the wrong transmitter. I have what I think is a 1996 502 ser # F602209. Can any on tell me what xmitter I need. Thanks.

Sounds like you need a new sending unit that goes with the new gauge you have.

^^^ Agree, you want a sender that is 240 ohms (low) and 33 ohm (high)

I'll bring my meter if I go pick one up, that range sounds about right. I think I need a merc part # 815425t

A VDO sender did the same thing with a Gaffrig gauge on my old boat.
The gauge should not peg when the key is turned on. It should go to 0.