The new sender (with a slightly longer float arm compared to one for a 20-gallon tank) simply installs in place of the old unit. Carefully place it inside the tank, and line up the unit's tabs with the notches in the tank. There are two notches that accept the tabs on the sender to correctly orient it in the tank. This ensures the float is in the right location and the fuel gauge is accurate. Be sure the sending unit is completely seated in the tank before reinstalling the retaining ring.