Read a Wiring Diagram

Whether you are working with a vehicle, appliance, light fixture, or receptacle, knowing how to read a wiring diagram will help you prevent personal injury or damage to the object on which you are working. It will show you the electric circuits within the object so you can complete your project safely.

Steps

  1. Find the wiring diagram. Wiring diagrams are often provided with appliances and other objects. However, they can be difficult to find. Look for a control panel, secret door, or on the back of an appliance. Look in the owner's manual when working on a vehicle. For other common objects, like receptacles (outlets) and light fixtures, check online.
  2. Check your voltage (V). Main lines are represented by L1, L2, and N. Look to see which main lines appear on your wiring diagram.
    • If your diagram has L1 and N, it is a 110V circuit.
    • If your diagram has both L1 and L2, it is a 240V circuit.
    • If your diagram has L1, L2, and N, it is a 110-240V circuit.
  3. Learn the symbols. Knowing what the symbols in your wiring diagram mean will help you find different lights, switches, and motors. Symbols usually resemble the part they represent. Familiarize yourself with descriptions for electrical appliances, understanding that different symbols appear for different objects.
    • Lights are shown as ovals with a squiggly line inside of them. They look like light bulbs. Different types of lights may be indicated with different symbols, such as a ceiling light versus recessed lighting.
    • Switches are symbolized by an opening or break in the line. It looks like the flip of a light switch.
    • Thermostats are symbolized by an opening or break in the line, but they also have a squiggle that connects them to the line.
    • A fuse is shown as a slight zigzag in the line.
    • Motors are shown as bumps along the line. It looks like an "M" with 5 or 6 humps.
  4. Know the color code. Different color wires represent different components. This makes testing different components within the system easier. There should be a key or legend on the wiring diagram to tell you what each color means. The specific colors for a home electrical system are generally the same across all electrical items.
    • White wires are neutral. They carry power back to the service panel.
    • Green or bare wires are the ground wires. These carry power back to the service panel in case the neutral wires fail.
    • Black, red, blue, and other colors represent hot wires. These are the ones that carry power to the object with which you are working.
    • Use a voltage tester if you are unsure what the different colors mean.

Tips

  • Turn off the source of all power to electrical systems before you begin your work. Then verify the power is off by using a voltage tester.
  • Call a licensed electrician if you have any questions or concerns. Working with electricity can be dangerous and only someone who knows what they are doing should attempt it.

Things You'll Need

  • Voltage tester

Sources and Citations

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