Read auto diagrams by following the color-coded schematic. An automotive diagram has separate colors for lighting, radio, ignition and secondary systems. If the diagram is printed in black and white or without a designated color pattern, the path or lines of the schematic show the difference between the systems.
Identify the electrical problem the automobile is having, such as a faulty brake light, and use the diagram to find the system that corresponds to the issue. Consult the car's repair manual and follow the steps to troubleshoot the problem. Typically, one of the steps leads to the damaged component or addresses a particular malfunction. Once the faulty part is found, make sure that the color of the wires in the diagram is identical to the color of the wires in the car. This is necessary for locating the power source or electrical circuit for the wire being fixed.
In many cases, schematics without color coding include small text beside each line that lists the color of the wire inside the car. The text is typically an abbreviation for a color, such as "GRN" representing green or "BLK" representing black.
Always test polarity using a circuit tester and disconnect the battery before starting work on a car's electrical system.