fuel gauge not working.

Just installed new tank,sending unit and fuel pump. When finished, I added 4 Gallons of gas. Now the fuel gauge is reading nothing. I reset computer and still nothing. When I'm coming to a stop the gauge will go up and right back down to nothing. Any ideas. thanks

Check the ground on both the sending unit, and the tank

i checked the grounds and wires. then i decided to put more gas in. that worked and now its working properly. thanks for your time.