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The relay location should be listed on the underside of the kick plate that needs to be removed to gain access to the relays. It is just a piece of paper glued on so it might not be there. If not someone else will chime in with a location for sure!

If you have fuel pressure then why are you checking the relay?

Ted makes the ultimate point. If you have pressure, the relay is obviously good.

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I've heard 2 different theories on the oil pressure switch.
#1 - is just like you said, if the oil pressure gets too low the fuel pump will quit getting power to save the engine.

#2 - is the the oil pressure switch is a redundant power supply so the engine won't stall if the fuel pump relay fails. I think this is the way it actually works. We have had a few members with very low oil pressure & the engine never quit.

Either way the engine shouldn't stall when you pull the relay.

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Here'* a wiring diagram.
Could you have damaged the wiring when you swapped engines?
What is your oil pressure reading?
With the key in the run position you should have 12 volts at the pink wire going to the oil pressure sender/switch. You could also connect a jumper between the pink & gray wire & then repeat your test. If it stalls something is wrong with the wiring. If it doesn't stall then the new sender is defective or the wrong P/N.

I'm not sure whats going on...
Does this mean the pcm only supples power to the relay during startup?
Other than that the pump will run if theres no oil pressure, which seems contray to whats desired, because power will still be supllied thru the relay.

Also pin 30 is normally power OUT not in. Not that it makes a big difference but why didn't GM follow industry standards?

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