1993 Chevy Silverado Fuel pump wont come on

Ok so one day I pull into a fast food place go in & eat come out and truck wont start so came back next day friend lisened and didnt hear the whirrr sound in the tank but tapped on the tank and it started so thought everything was fine but couple of days later pulled up to the house of the friend and after a couple of runs to the local convinent store it quit again so I went to replacing the fuel pump no whirrr sound and no fuel from the lines on the back of the throttle body / carb looking unit. Replaced fuel filter, pump, screen. No whirr sound checked all fueses in entire truck all are good none burnt or other wise unuseable. How does one check the relay for the fuel pump and or where is the fuel presure switch located would either of these prevent the fuel pump from comming on? I also did a check of the fuel sending unit several times before I put the tank back on & its fine so any other ideas thanks