something making a clicking/whiring noise..no fuel pressure

ok my 96 4.3l vin w blazer has been out of commission the past couple days....at first I thought it was the fuel pump but now im thinking it may be something else so I wanna narrow it down before i drop the tank....

when I turn the key to on, sometimes i wont hear the fuel pump priming and i dont get any fuel pressure at the test port, but occasionaly I will....the new sound i hear is a whiring/clicking noise directly behind the throttle body and i cant figure out what it is....what is there back there that would make a mechanical sounding noise when i put the key in the on position and it makes the same noise when i turn they key off again?

also, what sends the signal to the fuel pump to turn on/prime? is there maybe something thats keeping the fuel pump from turning on in the first place?

edit: also i already replaced the fuel pump relay

i tried checking what i think was the fuel pump prime wire....from a previous post it said it was the red wire in back of the engine compartment by brake booster, there was one thin guage wire with a connecter on the end and wasnt connected to anything, i tested that and got no voltage in key-on position. Also there was a thicker guage red wire that came from a bundle of wires that was routed over the top of the brake booster and it was connected to a bus above the wheel-well with a black plastic cover on it...got no voltage from that either.

so if one of those was my fuel pump prime wire, what is causing it to not get voltage?

also how do i check to see if my plugs are getting spark?

Do you Have paslock? It is a security feature built into your Blazer. What it does, it cuts off voltage to the fuel injectors when it feels that the right key is not being used. Read your owners manual it will give you a step by step instructions on the starting proceedure. Check to see if your security light stays on or flashes.