How to read the electrical diagram of a vehicle

In this video, we start with a problem on a Maxus Deliver 9 to understand how to read a vehicle's electrical diagram. The basic structure is represented by standard symbols (engine, sensor, relay), while the lines connecting them are the wires, often indicated with color codes or numbers; connectors are marked with circles/numbers (e.g., C204). The power supply is indicated as "+" or "30" (always active battery), while the grounds are marked as "-" or "31," often numbered (G101, G205). To follow a circuit, we need to identify the faulty component (for example, "fuel pump"), then find its symbol in the diagram and follow the line to the fuse, identified with a flame and a number, such as: F22. The relay is represented as a rectangle with a coil and contacts; the control unit is a rectangle with the abbreviation (e.g., ECM), while the ground is identified by a triangle or a Gxxxx. The key points for diagnosis are: "open circuit," meaning the interruption between two points (broken wire, corroded connector); "short to ground," meaning the wire touches the body (and the fuse blows). The tools we need are a multimeter to measure continuity and voltage; a test light to check for the presence of +12V; specific diagrams for the vehicle. The diagram reveals that multiple components share the same fuse, so we will look for the shorted component and proceed with its replacement: The diagram is followed starting from the power supply to reach the component and then to the ground.