The float inside the gasoline tank will rise or fall in response to the height of the fuel in the tank. Because of the movement of the metal rod concerning the float, the wiper included within the variable resistor is also allowed to move.
Each manufacturer designs its fuel-sending units to operate uniquely. whereas the fuel-sending unit on a GM vehicle of the same year will be the one closest to the ground when the tank is full. Consult the service handbook to understand how your vehicle's gasoline-sending unit reads the resistance.
On the resistive material strip, the windshield wiper will either be the closest to the ground or the farthest from the ground when the fuel tank is filled. This is either the point where there is the least amount of resistance or the maximum amount of resistance. When a vehicle is running on its last few drops of fuel, the wiper again is either closest to or furthest from the ground because the float rests at the bottom of the metal rods travel. The fuel gauge will display either full or empty, depending on the resistance. It reads as full or empty, which will vary depending on the specs of the gauge.
When the fuel level and the float drop in the tank, the metal rod connected to the float moves the wiper further away from the ground or closer to it, this either decreases or increases the electric current sent to the fuel gauge. The change in resistance causes the fuel gauge display to move away from the full position.