An efficient cooling system is essential in maintaining the engine’s performance under all operating conditions. Although the complete system will depend upon the individual installation, it is vital that the water pump and thermostat are working as designed.
The following schematic illustrates the 2003 Ford Focus Duratec RS Engine Cooling System Wiring Diagrams. The engine cooling electrical system consists of: battery, ignition switch, battery junction box, power hold relay, engine cooling fan relay, high speed engine cooling fan relay, powertrain control module, A/C high pressure switch, and cylinder-head temperature sensor. (click image to enlarge)