Truck won't start,checked the fuel pump relay and it clicks,removed fuel line from filter and no gas from fp when you crank.

Check fuel pump relay . Do you know what a relay is ? Go to your tube . Fuel Pump Electrical Test Relay and Fuse check Advance Auto Parts

No. Replace the Engine control unit that was destroyed when you reversed the polarity to it.

best thing to do is check for fuel and spark.your vechicle type has fuel filter in gas tank.remove fuel pump by removing rear seat cushion by pulling the seat stopprr near the floor and lift the cushion up.remove the pump inspection cover on the right side of the vechicle.then remove pump harness connector and fuel lines then remove fuel pump with fuel filter.

still won't crank ? how's your battery ? starter ? starter solonoid ? if your engine does'nt crank , its dead ! would'nt you check the battery first ? then move on with checking the starter circuit ? seems like your putting the cart before the horse ! first of all, when you run out of gas, you need to replace the FUEL FILTER, your engine just sucked the dirt, garbage, etc., out of the tank. there's plenty of sediment in the tank, don't know how it gets there, but, you'd be surprized ! talking threw experience !!! I operate heavy equipment, its a cardinal sin to run out of fuel !!! you say you replaced the inline filter, which one, up by the engine or the main filter, under vehicle along frame ? are we talking about the same animal, PLEASE CLARIFY !

Yes, it should. If it is conventional (like other GM cars), the pump will turn on for a couple of seconds when key is turned to on. This will prime the system for starting. When key is turned to start (cranking), the pump is turned on again at the relay, and pump stays on as long as cranking the engine happens. Once engine is started, the oil pressure switch keeps the pump running.
The best way to check if pump is good is to use a fuel pressure gauge. If it does not have a test port called a Schrader valve on the fuel rail, the pressure gauge must be teed in somewhere convenient. But if you take off the line at the filter, some gas should come out with key on, and when cranking the engine gas should come out in a steady stream.

I understand you replaced the relay but not the pump, right ?
Has the fuel filter been replaced recently ? Are you sure there is gas in the tank ?
You should be able to jumper the pump relay and check fuel pressure.

your doing the tests wrong (best I can tell)
most cars for sure USA.
the pump only runs key on for 1 or 3 seconds,called the injector PRIMING state. (keyed on only not cranked) and then....
and for sure the same relay closes full time , cranking or running.
so on dead engine all techs know this and crank at the same time measure the 2 power pins to the pump.
in your case it fails. I bet but that is the only test here.
next is the relay, most have 4 pins as yours does.
.
the PCM energizes the relay pump if you crank the starter
I can only assume cranking works all good?????
these rules in the PCM prevents crash and burn, like Ms Heche(RIP). did.
crash ,engine stalls and pump goes off line and not a huge fire. from broken fuel lines, and is USA law too this. safety
on some cars fuel relay goes off one if spark is lost and for sure injectors are shut down spark seen dead. all this is pure PCM logic. deep inside..
all this is covered in ASE classes to techs. how all this works
it's home users (DIY guys that do no know this ) so here is my lil' hints. late.
it does not work like say a swimming pool pump.sorry
2.2L engine.
oops this 2.2 L puppy has oil pressure switch that kills the pump fast after a short run of he engine, saving it.

all fuses must be good, top PCM too, f9/10
and check engine light good must glow key on or PCM is dead

the ecu enables fuel pump relay first. then oil pressure good susains the fuel pump relay.
so PCM F6 dark green/white wire is what energizes the FP relay coil.
if pump is dead (voltage dead) to pump cranking , no longer than 10seonds(not overheating starter)
and fall fuses are good. all as in ALL.
F6 wire at ECU/PCM is check next or at FP relay.
check all pins of FP relay for correct voltage cranked (dead engine STARTER Good)
and be fully aware of all ways the PCU will shut down the FP relay
not saying I know them all , it is Firmware logic in the PCM.

better photo here.

https://imgur.com/a/rB4j125

What do you mean it looks like its getting gas ? Try removeing the fuel filter its an in line filter located on the frame rail under the drivers door . Then put a plastic soda bottle on the line that is comeing from the gas tank and turn the key to run for 5 seconds . If you don't get at least 3 to 4 ounces of fuel then your fuel pump is bad . Or its the relay in the glove box or its the oil pressure sending uint . Have you been haveing problems with the oil pressure gauge or dose it start hard a long cranking time . Long cranking is the relay oil pressure problems is the sending unit but it is a back up power supply for the fuel pump . If the filter is clogged the pump is probably shot you could try replaceing the filter but that pump olny last 10 years at best it just depends if its been replaced at one time witch may be likely seenig its 20 years old the new ones were better a lot of upgrades on them check it out i can't do it for you olny you can do it good luck

check all your rounds on the body, behind kick panels, and in engine compartment. The relays you hear clicking are the power relay whcih turns your engine computer on. The other relay is the fuel pump relay, which is turned on by the engine computer. start there, report back.

PS. When you press the gas pedal to the floor during cranking, it shuts off the fuel supply to clear a flooded engine.

Check your fuel filter if it needs replacement. Empty it out then connect it back. Try to start it again. Inspect the fuel filter if it filled with gasoline. Check if there is noise at the fuel tank to check if the pump is working. If it did not, inspect the fuse for your fuel pump and the relay. If both are good you may connect the fuel pump directly to the battery to see if it works. It may be a bad wiring.