Okay I was have some issues a few months ago with my FSS and have purchased a new one ,bit before I install it I would like to know what the 2 wires do and how I go about testing them to make sure everything is good.

 

Apply power and ground to the two wires, and see if the linkage moves in. Make sure it pushes/pull hard, you should have a hard time fighting it.

 

1st Gen shut offs don't move any linkage. The best way to check it would be to start the truck, then disconnect the two wires that connect to it. If the truck doesn't shut off, the solenoid is your issue. Remove the solenoid and fish the plunger ans spring out of the pump. Inspect the plunger tip for rips or chips. If it has a rip or chip, there's the problem

 

Oops, I was thinking P-Pump style.