Gas Gauge Reads Backwards

Just had fuel pump and tank replaced from same model and year (89 cherokee) and as I drove it home, noticed the farther I went the more gas I had. Called the garage back and they said it is a polarized plug and they have no idea how to change it or why it reads that way. Anyone know which wires I can swap around (if possible) to make it read correctly? It appears to be 3 wires that come from the tank to the gauge and power for the pump. Thanks in advance!