* Fuel Sender Unit: This unit is located inside the fuel tank. It's a float attached to a variable resistor (rheostat). As the fuel level changes, the float moves, changing the resistance in the circuit. Low fuel means the float is low, and the resistance is high. Full fuel means the float is high, and the resistance is low.
* Wiring: This wiring connects the fuel sender unit to the fuel gauge in the dashboard.
* Fuel Gauge (Indicator): The fuel gauge is essentially a calibrated voltmeter or ammeter. It measures the resistance from the fuel sender and translates that resistance into a fuel level reading on the dial. A change in resistance (caused by the float's movement) causes a change in the voltage or current received by the gauge, moving the needle accordingly.
* Ground: A good ground connection is crucial. The circuit needs a complete path for the electricity to flow. A poor ground can cause inaccurate readings or a completely non-functional gauge.
In short, the changing fuel level moves a float, which alters the resistance, changing the signal to the gauge, which then displays the appropriate level. Any break in this chain (faulty sender, bad wiring, malfunctioning gauge, or poor ground) will prevent the gauge from working correctly.
