How to read electrical symbols for automobiles

Written by joanna swanson
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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.

Skill level:
Moderately Easy

Things you need

  • Automotive electrical diagram

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    Basic Symbols

  1. 1

    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.

  2. 2

    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.

  3. 3

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

  4. 4

    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.

    Wire Size, Color and Connection

  1. 1

    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.

  2. 2

    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.

  3. 3

    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.


  1. 1

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

  2. 2

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

  3. 3

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

  4. 4

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

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