The coolant temperature indicator system features a temperature gauge in the instrument panel and a coolant temperature sending unit on the cylinder head, with variations in location depending on the model type; carbureted models have the sending unit below the thermostat housing, while pre-OBD-II models place it on the intake manifold, and later models also use the intake manifold. Some vehicles may have multiple sending units, but only one is utilized for the gauge, while others serve as sensors for the air conditioning system or the Transmission Control Module (TCM). Fuel-injected vehicles include an Engine Coolant Temperature (ECT) sensor that monitors coolant temperature for the Powertrain Control Module (PCM), located in different positions based on engine type. To distinguish between a temperature sending unit and an ECT sensor, count the wires: sending units have one wire, while ECT sensors have two or three. In 1996 and later models, the ECT sensor acts as both the sending unit for the gauge and the information sensor for the PCM. In case of overheating, check the coolant level and ensure the wiring between the gauge and switch is secure, along with intact fuses. To test the circuit, ground the wire to the switch with the ignition on (engine off for safety); if the gauge deflects fully, the sending unit needs replacement. To replace the sending unit, unscrew it from the engine, apply sealant to the threads, and ensure the engine is cool before removal, as coolant will be lost during the process, so be ready to catch it and check the level after installation.