Inaccurate monitoring of fuel levels can lead to some dismal experiences. The level sensor in a vehicle’s fuel tank is actually a combination of three components; a float, an actuating rod and a resistor. This combination of components sends a variable signal to the fuel gauge or an electronic device — a “little black box” — that actuates the fuel gauge. The sensor assembly is often referred to as a sender. It is a relatively simple system once the function of each component part understood.
The float can be visualized by thinking of the ballcock in a lavatory cistern. The buoyant float — a sealed composite or metal ellipsoid, or a foam solid — is typically oval rather than circular and rests on the surface of the fuel. It is attached to a pivoted actuating rod.