This section describes the operating principles of sending units, warning lights and gauges. Sensors that provide information to the Electronic Control Module (ECM) are covered in Driveability & Emissions Controls of this guide.
Several types of sending units exist, however most can be characterized as being either a pressure type or a resistance type. Pressure type sending units convert liquid pressure into an electrical signal that is sent to the gauge. Resistance type sending units are most often used to measure temperature and use variable resistance to control the current flow back to the indicating device. Both types of sending units are connected in series by a wire to the battery (through the ignition switch). When the ignition is turned ON , current flows from the battery through the indicating device and on to the sending unit.