The Role Wiring Diagrams Play in the Troubleshooting Process
When dealing with an electrical problem in your vehicle, the first place you may turn is to the manufacturer's wiring diagram. Most people assume that since the wiring diagram gives you a blueprint of the vehicle's electrical system, that they will soon be able to identify the inoperable circuit. This is not always the case.
These wiring diagrams can show the entire lighting system with all its circuits, or even the complete electrical system for the whole vehicle. Relying on the wiring diagram to positively identify your inoperable circuit is very often unrealistic. Also, if your vehicle has had any electrical work done or auto body work done, than these diagrams could also be inaccurate.
The bottom line is that manufacturers' wiring diagrams will not identify or isolate inoperable circuits for you. In the end it will take your troubleshooting skills to identify the problem.