Fuel Tank Crossover Valve

[JJAB]

I know this subject has been discussed a thousand times. I put a LS 5.3 into my 1987 C10. Decided to run an external pump on the frame rail. Here lies my problem. Quite naturally all sensors and stock injects were unplugged to install the 5.3. Fast forward... I have looked at many schematics and I have come to understand that the tan/white wire coming from the fuel pump relay on the fire wall powers the tank selctor switch inside the cab and it also powers the tank crossover valve under the truck. Further understanding of the schematic led to learning that the tan/white wire only powers when the oil pressure switch reads at least 12lbs of oil pressure. Problem is, the original oil pressure switch is no longer plugged to anything. I attempted to jump the oil pressure switch wires but this did not work

Also, there is another tan/white wire coming from that harness that looks like it should be grounded, but it has 12v???????. How do I bypass the oil pressure switch to power the selector switch and valve?