Locating an electrical short in a car or truck can be difficult and time-consuming.
But by using a simple test light method, you can narrow your search dramatically.
This process will save you time and money and is a quick way to find an electrical short in almost any vehicle.
Using a 12-volt test light, as shown below, you can locate any short or parasitic draw.
Example 12-Volt Test Light on Amazon
ATD Tools 5513 Heavy-Duty Circuit Tester
Steps to Find an Electrical Short on a Vehicle
- First, disconnect the negative or positive battery terminal.
- Clip the end of the test light to the battery terminal.
- Place the other end of the test light on the terminal.
- If there is a short or electrical draw, the test light will light up.
- Next, open up your fuse panel.
- One-by-one, pull a fuse. As you pull a fuse, look at the test light. If the light stays on, put the fuse back in and pull another.
- Continue pulling and testing your fuses until the light goes out.
- Once the light goes out, look at the circuit that the fuse controls, and it will tell you what the short is.
How To Find an Electrical Short in a Vehicle Explained
A vehicle’s electrical system is divided into sections such as the ignition, charging, lights, and so on.
Each section has a fuse that, when removed, shuts it down.
If you pull a fuse and the light goes out, then this will be the circuit that will have the short.
Look at what circuit the fuse is on, for example, lights, and that will point to where the issue is located.
Each fuse box can be different, sometimes with a number, other times clearly labeled with the circuit.
For example, if the fuse you pulled out has a number 15 next to the holes, then the short will be on circuit 15. Now flip over your fuse box panel cover.
After flipping over your fuse block panel cover, you will see the numbers in order. Locate your fuse number, in this case, circuit number 15. Next to the number 15, you will see the circuit name.
An example would be 14 tail lights, 15 cigarette lighter, and so on.
So, for example, because the light that went out was fuse number 15, and fuse number 15 is the fuse for the cigarette lighter. The short is in the cigarette lighter or the wiring for the cigarette lighter.
In this example, we would follow the wiring looking for any melted spots on the wire or looking inside the cigarette lighter for any type of melting.
The same can be done with any circuit in a car or truck, such as headlights, taillights, radio, or most any circuit in a vehicle.
This process will narrow your search greatly from hundreds of possible wires to a few wires in minutes.
Components that Could Cause a Miss-read
- The door light is on.
- the radio clock is on.
- The key is on accessory.
To stop a miss-read, pull the fuses for anything on when the key is off.
Simply look at the fuse box cover and remove the fuse for those items while performing this test.
For example, If the radio is on when the key is off and on fuse number 26, then remove fuse number 26 until the test is over. Then replace it with the same fuse.
When removing fuses, it is usually best to only pull one or a few at a time since they need to go back into the correct spot.
You do not want a 30 amp fuse in a 5 amp location.
To avoid this issue, only pull one at a time, write it down, or simply take a picture of the fuse box before removing any fuses.
So, in short, disconnect the battery connect the test light to the terminal and the battery. Pull fuses one by one until the light goes out.
Follow the fuse box cover number to the name of the circuit. Then follow the wiring, and replace anything that is melted.
Signs and Symptoms of a Vehicle Short
- Low voltage when trying to start your car. (Long cranking time).
- Lights dim while cranking the engine over.
- Needing a jump in the mornings or when the vehicle has not been started for long periods of time.
If you have any or all of these symptoms, you could have a short.
Common Vehicle Electrical Shorts
- Cigarette lighters (We tend to overload this circuit with our gadgets)
- Busted lights ( If this is the fuse, check for any broken light)
- Aftermarket radios.
- Aftermarket amplifiers.
- Any wires that hang low around your feet area of the car.
Use your senses when trying to locate the issue, smell for burnt wires and look for anything that is melted.
Most shorts, you can locate yourself. Some mechanics will tell you that you should never disconnect your battery terminal because the computer will lose its memory.
Do not be afraid to disconnect the terminal. The computer will reset. The computer will behave so just as if your battery was bad and you needed to replace it.
However, you may need to reset your clock and reprogram all your favorite radio stations. Do not leave a short unfixed, hoping it will go away. Fixing a short keeps your family and friends safe and makes a happy car.
Remember, if in doubt, take your car or truck to a professional.