If the tank was part of the work, it could be that the fuel float wasn't positioned correctly when it was reassembled. I got mine back from the delaer once with float installed backwards. The float arm is supposed to ride in a channel on the switch itself; if it isn't, then whatever position the switch is in will be your constant fuel level. After you've exhausted the electrical checks, drain the fuel and remove the fuel level sender - check that the float arm is installed in the switch channel, then reassemble.