Now hook the light up to the fuel pump relay, or whatever the diagram says. And so on ...

 

if the fuse that controls the fuel pump electrics is good, the fact that you get noise in the fuel pump when u juggle the ignition key back and forth suggests to me that the fuel pump is not being energized when the ignition key is in 'run.' short? bad ground ?

on my 3500 07 express the ignition switch was finicky and van eventually wouldn't turn on at all, i had to replace the switch. at the same time the obd2 reader under the dash was working only intermittently and with both of these problems being intermittent it was a night mare to diagnose. after th ign sw replace i still had no read from obd2 which the fancy expensive obd2 reader diagnosed as a bad obd2 receptacle.

by the way i swear the ignition switch failed because the spouse carried (past tense) about a pound of keys on the keychain with the chevy key.

 

That's a good point. I think the ignition switch is a common problem with GMs. You could try skipping right to that.

https://www.aa1car.com/library/ignition_switch.htm