That should be a TBI (Throttle Body Injection) and not a carburetor. I think 85 was the last year for Carbs in S trucks (2.8L).
You should be able to hear the pump run for about 2 seconds when you first turn the key on (wait a few seconds when turning the key off and on to hear pump run). If you don't hear the pump run then there could be a bad relay or its circuit.
The relay should be on the firewall. Have a helper listen for a relay to click. A person can even feel a relay click when the key is turned on if its working.The computer sends a ground signal to the relay to activate it.
But the oil pressure switch also is part of the circuit. When the truck has oil pressure the switch will send power to the fuel pump.
So even if you had it running with gas being poured in the TB, that could have been long enough to build oil pressure (as long as the switch is good)
Then check your connections at the sender. There is also a ground wire on the frame. I think it is near the filler hose just about behind the bracket the bed sits on. Make sure there is a good ground.
You can look up free diagrams at autozone.com. All you have to do is register and that is free as well. That should help you follow the circuit for the pump.
I would say more than likely your problem is a clogged fuel filter or a bad fuel pump. To narrow this down, listen for the fuel pump 'priming' (making a whining noise from the gas tank) turn the key to the On position and you should hear this whining for about 3 seconds, if you can hear this the fuel pump works fine, if not it is probably time for a new one. As for the fuel filter being that it is a 1987, I would replace it even if it is not clogged, the easiest way to test if it is clogged though is to blow at through it with your mouth and if you feel any resistance then it needs replacing.
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