To read a diagram for automotive repair, first locate the problem, and then use the legend or text that describes which wire color is designated to which system. Each color corresponds to the actual color on the wires in the vehicle. Automotive repair diagrams typically include illustrations for the vehicle's lighting, radio, ignition and secondary systems.
After you determine which system is affected, locate that system's area on the diagram using the corresponding system color. Use a repair manual or tutorial to troubleshoot which component in the system is causing the problem. Find the component on the diagram using labels or shapes, and follow the color code to locate the component's power source or electrical circuit. If you are unsure about the symbols and labels, follow electrician standards.
Occasionally, the diagram may be in black and white instead of color. Some black and white diagrams include small text next to or over the wires with an abbreviation of the wire's color. For example, the color green is represented by "GRN," and the color black is written as "BLK." Before starting the repair, check polarity using a circuit tester. Always disconnect the car battery before attempting any repairs to electrical wires.