thanks.
looking at the wiring, it looks like the fuel pump relay and oil press sender are wired parallel. So i would say that if the oil sensor reads low, it shorts the power to ground and you lose power to the fuel pump.
The oil pressure sender and the fuel pump relay are definitely wired in parallel, but the circuit does not act as a fail safe for low oil pressure. The parallel circuit allows the truck to still start if the relay is bad.
I remember DaveP mentioning this a few times.
I removed that circuit when I did the XFI. You can leave the (middle?) wire on the sensor\switch to keep the gauge working.