2000 silverado 1500

I want to answer the e-mail about changing the fuel pump relay, and the answer is yes , I changed the relay and then the ignition switch but I still have the problem so I took my voltmeter and check for power at the relay socket and foun no power so I place a jumper from the positive of the battery to the relay and feed power to the fuel pump which ran fine and the engine ran good, then I replace the relay and the next day I try againg by crancking the engine as if nathing was rwong and it ran good, so What can cause this problem? the question remains the same.Thanks for your help