Fuel sender issue

I installed a Tanks Inc tank with in tank E fuel pump in my 72 Duster . I have an odd problem , when I set sender and fuel pump in I tied the grounds together thinking this would work fine . My fuel pump works fine but I'm not getting signal to my fuel gauge so after checking the cluster and finding nothing obvious I turn to the sender . I had my wife sit in the car and turn the key on while probed around with a temporary ground and my gauge started working . The tank is in the car and I'm working pretty much blind so I can't see what I was touching with the temporary ground but I figured there must be an issue with the ground being tied into the fuel pump ( I know makes no sense) . So I install a dedicated ground for the sender and I get zero reading again . Any thoughts ?