00 how to trouble shoot fuel sender

ok so I finally got the fuel tank in and on this truck you cant put a fuel tank from just under neath the box has to come out if your doing the fuel tank

but my problem is the fuel sender isn't sending info to the dash or cable is broken

I guessing its the 2nd connector on the pump the 3 wire? and how can I trouble shoot that to see if its working etc

this is a brand new tank and fuel pump