How to Read Car Wiring Diagrams

Updated April 17, 2017

A wiring diagram or schematic visually represents the way that a circuit is constructed. A typical automotive wiring diagram represents a single system of your vehicle. For instance a wiring diagram for your vehicle might represent the interior lighting system. When you are having electrical issues with your car, it is a useful skill to know how to read these diagrams. Remember that the diagrams are not literal drawings of the locations of electrical parts, but symbolise the parts and connections.

Obtain a sample wiring diagram representing a system of a vehicle. Try factory repair manuals, websites, or your vehicle's owner's manual as a source for a diagram.

Learn the symbols for the basic components on a wiring diagram; these are the switch, resistor, ground point, and battery. Remember the standard variations that exist for the battery (variable battery) symbol and the ground (case ground) symbol .

Memorise what the advanced component symbols look like and what the labels near them stand for. They might be used to designate component positive and negative terminals, component pin numbers, or component electrical or circuit values. Obtain a guide with a full listing of symbols if you come across a schematic with something that is not labelled.

Learn how the wires and connections are drawn. Remember a dot symbolises that two wires are connected, while a wire with no dot symbolises wires that cross physically but are not connected. Note that the notations like "BRN/WHT" or "LT GRN" denote the colours of the wires themselves.


Always check fuses and relays before attempting to use a wiring diagram to check components or connections.

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About the Author

David Somerset has been a writer intermittently for 11 years. He attended New Mexico Tech and earned a Bachelor of Science in technical communication in 2007. From being published in the "Bucksworth Community News" to writing how-to articles for eHow, his experience is quite diverse.