How to Find a 12 Volt Wiring Short

Written by jonra springs
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How to Find a 12 Volt Wiring Short
Digital multimeter with attached leads (digital multimeter 3 image by dinostock from

The electrical wiring in 12-volt systems, such as those in cars and boats, is subject to several damage hazards that can create shorts and stop on-board appliances from working. Automotive wiring under the hood is exposed to heat and corrosive fluids. Some marine wiring is not concealed well enough to prevent it from becoming damaged by other items in the boat. Test the wiring for a short the next time something stops working in your car or boat.

Skill level:

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Things you need

  • Adjustable wrench
  • Wiring schematics
  • Multimeter
  • Lead extensions

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  1. 1

    Turn off the motor and unhook the battery. Remove the positive terminal from the 12-volt battery by loosening the terminal bolt with an adjustable wrench. Pull the cable away from the battery to prevent the terminal from making contact with the positive post.

  2. 2

    Refer to the wiring schematic for 12-volt electrical systems in boats and cars to find all the electrical wiring involved in the non-functioning device. Locate each of the physical wires in the car or boat that are shown in the wiring diagram.

  3. 3

    Set a multimeter to "ohms" to perform continuity tests on each of the wires. Zero out the ohms scale on an analogue multimeter by touching the leads together and setting the needle on zero with the calibrating wheel or dial.

  4. 4

    Touch one lead to one end of a wire and the other lead to the other end. Avoid touching the leads while taking a reading, as your skin will affect the resistance being measured. Use long lead extension wires with alligator clip ends if necessary for reaching both ends of long wires.

  5. 5

    Read the ohms values shown on the meter display. A reading reflected by any number shows a good wire. An infinite reading shows a short in the wire. Replace any wire that proves to have a short with this test to restore service to the on-board appliance.

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