I installed a new oil pressure sending unit on a 56 Merc. with a 292 cu. in. ( not a 312). I can't get it to read the oil pressure in the engine. I connected a mechanical gage and it records good pressure (65 to 70psi) The sending unit I used has a dual post on top of it and I only have one wire running from my gage. When I ground the wire with the key on the gage goes all the way to max. So its getting voltage. I don't know why they put a dual post on top of the sending unit or why my gage wouldn't register any pressure. Does anybody know what I could check out?

thanks, Tom

roviwancanobe