I'm confused and not sure what direction to go. 99 Zr2, new ac delco fuel pump, bench tested, works. 11 volts for 2 sec. at the harness(gray wire). Grounds show good circuits. Plug harness into pump and it won't run. WTF?

 

i hate to say it but have you checked harness for broken wires...or maybe the connector is bad.
just my first thoughts.

 

Just bypassed connector ground directly to the frame and everything works.

 

Love it when a plan comes together.