Joe,
Usually these sensors have a resistance range of operation with and without fluid on the sensor. You could look for literature on that sensor from the manufacturer, take some ohm measurements and see if it is wiring or the new sensor that is at fault. One of the wires on it should go to ground. You could measure from that wire to a metal chassis ground to see that you are getting a good ground. If the tank is metal and that is used as a ground be sure that the sealant on the plug, Teflon tape or otherwise is not fully insulating it. Could be that you got a bad sensor as a replacement. The hot lead to the sensor will have a voltage on it with the ignition on, you could measure that voltage and have someone else with the same tank sensor take measurements to compare. Hope this helps.
Later Ed
