82Brlinetta

Hi there. I've got an 82 Berlinetta I just bought and the fuel gauge doesn't work. It sits almost vertical, a mm or two to the left, but gently floats to dead vertical when the car is on. Guy told me he just replaced the fuel tank. I looked under the car, and the three pin connector is just hanging off the top of the fuel tank. The car runs and drives but has no power unless I pump the gas pedal. I've looked for the connector that is supposed to be behind the rear drivers side seat, but its just bare metal. Please help me find where the connector is so I don't get stranded with no gas!