Can you post the page of the manual that shows the fuel pump electrical circuit? What part of the circuit have you checked so far?
You want to troubleshoot when it is working (and write down what you see/confirm it matches the circuit. Obviously, the best time to troubleshoot is when the truck does not start (because you can see what's different from expected behavior:measurements.
To troubleshoot electrical issue a voltmeter is best (you did not say how you are doing your troubleshooting. A wire + bulb can also work in many cases ).
1995 D90 NAS
1996 Discovery NAS
2006 LR3 NAS (hers, but comfy! :) )