How to read electrical symbols for automobiles

Updated April 17, 2017

On an automotive wiring diagram, symbols are used to convey the locations and types of the components used in the car's wiring. These symbols can be confusing unless you can learn how to read them. Most automotive wiring diagrams use the same standard electrical symbols to show the location of basic components such as switches and batteries. Other symbols denote wire size and colour, or serve as an abbreviation for a common electrical term.

Locate a switch by finding an arrow that interrupts the straight line of a wire by angling away from the line. This arrow points to a box. A dotted line curves from this box back to the wire to show that a circuit is completed when the switch is shut.

Find a battery by locating a series of four lines perpendicular to the wiring. These lines alternate a long line with a short line. The wiring continues after this set of lines.

To find a resistor, look for a line that zigzags back and forth with three peaks on each side of the line.

A ground is located by looking for the wire that ends at a dot with the code "G100" next to it. The dot appears to be sitting on three small lines that get gradually shorter.

Find the diameter of the wire by locating a number placed next to the wire. This number generally precedes a code for the colour of the wire.

Locate the colour of the wire by finding the three letter code for the colour printed near the wire marking on the diagram. An example of this code is "BLK" for black.

Follow a wire until it meets another wire. A connection is designated by a dot. If the wires cross and are not connected, one wire will appear to bump up over the other wire and no dot is printed.

The amperage of a wiring circuit is found by locating the letter "A" printed beside a number.

Find the pass-through grommet by locating the symbol "P100."

Find the symbol "C1." This symbol stands for the terminal connector identification.

Locate the symbol "B+." This also designates a battery connection.

Things You'll Need

  • Automotive electrical diagram
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About the Author

Based in Laramie, Wyo., Joanna Swanson has been writing in her professional life since 2004. She currently writes for various websites and enjoys reading a wide variety of books. Swanson holds a bachelor's degree in business administration from the University of Wyoming.