[Desert1957]

I think your truck (If an 87) should be like mine. On the firewall there should be two relays. Not sure without looking which one is fuel pump relay. I will have to check the other pages in the wiring books I have to figure out if that is the signal wire from the relay to the switching valve. I think it almost has to be.
Just remember in theory what a relay does. Anything with a motor or a high amp draw (like a fuel pump) have a switching relay to prevent the wiring from having problems.

So back to your question, You want to know if the relay wire from the firewall , goes to the switching valve and then to the pump?

I will do the research today , might not post until wed PM...
Desert