electric fuel pump oil pressure switch pins gauge

Be specific......................

1---WHAT are we workin on, IE make, model and year

(What you have in your avatar doesn't look like any A body, to me, and even if it did...............)

2---WHAT exactly did you use for a 3 prong oil sender? For all I know you have a sender that should be feeding a warning light, not a gauge.

3---How do you know you have the sender wired correctly? Where did you figure this out? Can you/ did you measure the resistance of the sender for the gauge section, even with no pressure?