How to Find a Short Circuit in an Auto Electrical System

Written by angus koolbreeze
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How to Find a Short Circuit in an Auto Electrical System
Check your car's electrical system thoroughly, especially when you suspect a short. (red car image by Viachaslau Makouski from

A short circuit is one that completes itself the wrong way (e.g., when two bare wires touch each other), causing the current finds a path of least resistance and bypasses the normal flow route. This causes a current flow too great for the electrical system of your vehicle to handle. As a result, fuses begin to blow, and other components begin to overheat. Other problems include melted wires, causing an open circuit. Testing and diagnostic measures are in order when your vehicle's electrical system has a short circuit.

Skill level:

Things you need

  • Test light
  • Long cord

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  1. 1

    Check your battery. As the Second Chance Garage website states, the battery is the heart of your electrical system. If necessary, fully charge the battery and check for signs of corrosion. If your problem is the battery, change it before executing another step.

  2. 2

    Make a test light with about 15 feet of cord. Depending on the size of your car, you may need to make it longer. Make this cord of sufficient length to comfortably manoeuvre around your car.

  3. 3

    Place alligator clips on one end and a stop/tail light on the other. Wire both filaments together to obtain a current drain, which will help you acquire a more accurate test result.

  4. 4

    Insulate all exposed connections, including the body of the lamp itself. Wrap insulation tape around the connections.

  5. 5

    Place your test lamp across the circuit you suspect has gone bad.

  6. 6

    Turn on the part of the car you suspect that has the compromised circuit function. If it is your ignition, turn on your vehicle. If the test light comes on, and it shines steadily, then you have found your short.

Tips and warnings

  • When checking headlight circuits, the test light will not dim as much because of the lower resistance of this particular circuit. According to the Lotus Elan website, this is in conformity with Ohm's law, which says that "the sum of voltage drops must equal the supply voltage."
  • According to the Lotus Elan website, be sure to properly insulate your test light, because that is the only way to ensure safety of the process. Furthermore, if you have any doubts about using these devices, leave the testing, diagnosis, and corrective processes to the trained car professionals.

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