The fuel level sensor sends a varying signal to the fuel gauge or electronic gadget that triggers the fuel gauge. The components of the sensor, such as float, rod and resistor, work together to give a reading on the level of fuel.
The sensor assembly acts as the sender. The float is on top of the fuel and links to a pivoted activating rod. It moves up and down to match the level of fuel.
The rod moves with the float. The other end of the rod has a grounded resistor. The battery supplies power to the resistor. A wire runs from the resistor to the fuel gauge or electronic device that interprets the signal to indicate the fuel level.
The movement of the rod affects a tiny wiper in the resistor. The wiper moves along a resistant strip with a grounded end. When it is far from the grounded end, it conducts less electricity than in the reverse situation. The resistance is also high at this point, which coincides with an empty tank.
The signal is at the peak when the tank is full and begins to drop as the fuel level drops. During this time, the float drops, and the rod pulls the wiper away from the ground; therefore, less current passes to the gauge. The needle shows a drop in the fuel level.
The float normally reads a full tank before the tank gets full. Therefore, it takes time for the needle to start dropping while driving.