[Barnsnake]

Bob:
The previous owner may have installed the sender turned the wrong direction or, more likely, bent the float arm during installation. He may also have installed a replacement sender with the wrong resistance range.
Most senders are variable resistors moved by a float on the end of a wire arm. It should be verified that the arm can move freely in the tank without striking obstructions, like baffles or return tubes. To calibrate the sender you bend the arm so the float is at the bottom of the tank at the bottom of its travel, and at the top of the tank at the top of the sender travel. Many senders have a telescopic section to accommodate various tank depths, while others pivot at the top and have a longer float arm that must be cut and/or bent to match the tank depth.
Remove the sender and attach a ohm meter to the sender post and the mounting plate. Move the float arm through its range and note the resistance. It should smoothly change resistance throughout the travel. Verify that the resistance range matches the specified range for your gauge. Measure the depth of the tank at the sender location and bend (or otherwise adjust) the float arm to that the top of the float is full up when 1/8"-1/4" below the plane of the mounting plate and fully down when the bottom of the float is at tank depth below the mounting plate. Make sure it is pointing in a direction free of obstructions when reinstalled.