What causes the electrical signal change in a variable resistor type fuel contents gauge?

• A. The change in ambient temperature.
• B. The change in fuel contents causes a change in current in the circuit.
• C. A change in atmospheric pressure.
• D. A change in tank orientation.

Answer: (B)

In a variable resistor fuel gauge, the fuel level moves a float that changes the position of a wiper on a resistive element, effectively altering the resistance in the circuit. Because the circuit is powered by a fixed voltage, that change in resistance produces a different current through the gauge. The indicator is calibrated so this current (or the corresponding voltage) corresponds to the amount of fuel, so the reading tracks fuel quantity as the resistance changes with fuel level.

Ambient temperature might cause small resistance shifts, but the gauge is designed to rely on the float-driven resistance change, not temperature. Atmospheric pressure doesn’t affect the electrical signal in this setup, and tank orientation can influence float motion only in extreme angles, not the fundamental mechanism. The essential point is that the fuel level changes resistance, which changes current, and the instrument reads that current to display fuel quantity.