i'm trying to get my sending unit wired up and all the diagrams that i see show the 86-89 with just dummy lights. i got a gauge and i want to use it. how do i wire it up? BTW my sending unit is the one with the connector that looks like pac man with his nose and lip pierced lol

Whose gauge is it?
Often you have to use the sender unit made by the gauge maker, not a OEM one.
How many pins on your sender unit?

Those engines used a "mechanical" oil pressure sending unit fed thru brass fittings to a canister type sending unit. The early version of the fuel cutoff sending unit only had 2 pins. The later ones ( 91-92 ) had 3 Pins. The 3rd pin is for the gauge wire.

I mistakenly installed a 2 pin 88 sending unit into my 91 last fall. As a result the car ran fine - but I had no reading from the gauge. Installed the 3 pin sending unit and I was good to go.

If your car doesn't have 3 wires on the plug - you could get a plug/pigtail and run your sending unit wire to it.

ok. my sonoma has the 3 pin plug/sending unit. but i need to make sure this is still gonna run the cut off switch..

It is not a cut off switch.
It is the switch that makes the fuel pump run when cranking and a backup for the fuel pump relay.
Would be easiest to install a T at that location and run a seperate sender for the gauge

so i should cut off my original fuel pump relay wires and splice in the switch? (run it like factory)?

Don't mean to hijack the thread but I've got a question about the 3 prong plug that no one wants to answer.If I'm looking at the 3 prong plug top termanal is B(tan),bottom left(D)gray,and bottom right(C) orange.Am I correct?

yes. it should look like a 3/4 pie cut on the connector

i'm just gonna put in a new harness and splice in the old sending unit...

i cannot get my fuel pressure relieved after pulling fuel pump fuse. wandering if i pull the power wire from my oil pressure switch, will it shut off fuel pump relay. i have read that the oil press switch doubles as a "relay" for fuel pump. any help welcome.

@irocz it (OPS) is backup power to the FP, it closes at 4psi (cranking oil press).
just unplug it, start the engine and fuel pressure should drop to 0psi almost immediately. engine will die shortly after.

The ECM triggers the FP during crank (the instant it gets a tach signal).

The OPS is backup for relay failure only and can be omitted from the wiring if desired.