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Fuel pump only gets 2 seconds of power when key is turned to ON, then no more power until engine starts, OR, you turn key OFF and then ON again, then 2 second of power again.
So you can only "test for power" for those 2 seconds.
Fuel pump power comes from a 30 amp fuse in the engine fuse box and it travels like this:
Battery--------30 amp fuse---------fuel pump relay-------inertia switch----------fuel pump---Ground
Fuel pump relay will be on inner fender and will have a Green Base/Plugin, in '89 it could be under the engine fuse box with 2 other relays
inertia switch will be in the cab, passenger side just below glove box or in the kick panel, is it a small black plastic square with a button on the top.
If truck stops suddenly or rolls over inertia switch will OPEN and cut power to fuel pump.
Button the the top resets it.
If you have a volt meter then find the fuel pump relay, unplug the relay from its base.
Key off
Test each hole in the base for 12volts, that 12volts is from the 30 amp fuse, has power 24/7, no 12v then blown fuse.
Now turn key ON
test each hole, should now be a second one with 12volts.