The Block Diagram shows the basic connection paths used for successful operation. The arrows indicate the primary direction of the control or communication. It is important to consider the Engine & ECU Wiring harness complete with all associated sensors as a complete single unit. While some parts of the Engine & ECU Wiring Harness may need to be adapted to suit your vehicle configuration the overall harness should not be varied greatly. For details of individual sensor wiring refer to the electronic version of the Ford Focus Wiring Diagrams.
The OEM Engine Control Unit is designed to be located within the engine bay and only needs to be mounted with the connectors protected from direct water ingress.