A video is at the bottom of the page for a visual walk-through if needed.
The process of locating an electrical short can be difficult and time-consuming.
By using a simple test light method you can narrow your search dramatically.
This process will save you time and money.
12 Volt Test Light on Amazon
ATD Tools 5513 Heavy-Duty Circuit Tester
Signs of a Short
- Low voltage when trying to start your car. (Longer 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.
Using a 12-volt test light as shown below you can locate most shorts.
Steps to Find an Electrical Short on a Vehicle
- First, disconnect the negative battery terminal.
- Clip the end of the test light to the negative side of the battery terminal.
- Place the other end of the test light on the negative terminal. If there is a short 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 fuse controls and it will tell you what is the short.
Lets explain an example.
If you pull a fuse and the light goes out. This will be the circuit that will have the short. Look where you pulled the fuse for the circuit it is on.
Each fuse box can be different sometimes with a number other times clearly labeled with the circuit.
Let’s say 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, the 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 look 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, tail-lights, 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.
Some items that could cause a miss-read are as followed.
- Your door light is on.
- Your radio clock is on.
- Your key is on, or on the 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.
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 2 major senses when trying to locate the issue.
- Smell for burnt wires
- Look for things that are melted
75 percent of your 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. This issue can cause harm to your car. 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.