The wiring diagram is important to troubleshoot the problem in the car. This video explains how to use wiring diagram to fix a problem. The wiring diagram contain the information of wiring path of the application in the car like heater, AC, Tachometer and so on. First, the wiring diagram must be fotocopied. Then give the highlight where the problem occurred. Then trace the wire which feed the appication that gives the problem. So we can know the porblem source that make the application malfunction. Fix the block that feed the application. Here is the video: