Gas Gauge Reads Half A Tank But The Fuel Light Turns On And It Is Low On Fuel.

If it still doesn't work after you replaced and adjusted the float, you will have to replace the complete sending unit. The sending unit operates on electrical resistance. It's basically a piece of negatively grounded metal that scrapes along another piece of metal that has a low level of electrical current going through it. The higher the float level, the lower the resistance. As the float levels lowers, the more resistance you have and that makes the fuel gauge go lower. The metal piece can break off or corrode over time, so that's why it is no longer reading the fuel level accurately.