Adding an OE electrical oil pressure gauge to a 71-76 A-body cluster?

j_anderson said

I would use a nylon hat washer that's sized to the diameter of those bulb holder holes and run the gauge posts through them and hold them in with some speed nuts like the ones on the fuel/temp/ammeter gauge posts.
Jumper from oil send trace to appropriate post on gauge. Jumper ground to the other post.

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The gauge doesn't connect to sender and ground- the sender is a variable ground. The gauge gets a 12v feed and grounds through the sender (which varies depending on oil pressure, which gives you your gauge reading). So, 12v from the panel cluster (fuel and temp are regulated by the IVR to ~5v, so don't use those) and the sender wire would be your 2 connections.