You need a voltmeter to read the codes, and an ohmeter to see if the wires have continuity.

Download the factory shop manual for your truck, or the closest thing to it, like an 89. Look both at the wiring diagrams and the harness layout diagrams to trace your wiring from the control relay to the fuel pump. The wiring diagram will show wire sizes and colors, and connector numbers. The harness diagrams will show connector locations and harness routes. I'd start at the fuel pump and work back to the relay. Very easy to have a corroded connector or broken wire under the truck, or under the passenger carpet or back seats.

The intro to the electrical section will show you connector shape codes, wire color codes, how to find shorts and broken wires, and mucho other useful stuff, like how to read the diagrams, electrical gizmo symbols, and suchlike stuff.

If the pump runs when removed, it's a wiring or relay problem, or the pump ground wire. I'm suspecting the latter, but check it all.