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How To Find A Broken Wire In An Auto Wire Harness

To ensure the proper functioning of your auto wiring harness, it’s important to perform regular maintenance, which includes regularly inspecting for broken or loose connections and replacing damaged or old wires. The article below will discuss how to find a broken wire in an auto-wiring harness.

Table of Contents

How Long Should an Auto Wiring Harness Last?

The lifespan of your vehicle wires depends on several factors, such as the manufacturing process, usage patterns, environmental conditions, and the materials’ quality.

 Generally, a properly made harness should last long, if not your car’s entire lifespan.

The wiring harness can last up to 20 years or more for automotive applications without exposure to excessive moisture, physical damage, or heat.

What Causes a Broken Auto Wiring Harness?

Below are the five main causes of a broken auto wiring harness.

Manufacturing Defects

Manufacturing defects could be incorrect assembly, inadequate insulation, or low-quality materials.


Exposure to road salt, moisture, or other components could corrode the connectors, wires, or terminals.

Vibration and Physical Damage

Constant vibration from rough road conditions or your car’s engine could cause the wires to rub on each other or surrounding components, causing the insulation to wear or break the wires. 

Also, physical damage could occur due to collision or improper handling when installing or maintaining.

Heat and Thermal Degradation

When exposed to high temperatures, the wires could suffer from thermal degradation, leading to wire damage and insulation breakdown.

Rodent Damage

Rodents such as rats and mice could also be an unlikely cause of wire harness issues. 

They can chew through the insulation and wires, causing open circuits, intermittent connections, or short circuits. 

Rodent damage is difficult to handle as it occurs in hard-to-reach or hidden areas.

Rodent Damaging Car Wires

Caption: Rodent Damaging Car Wires

Bad Effects of A Broken Wire in an Auto Wiring Harness

Although your car’s electronic system could fail, you likely have an electrical gremlin. Often, this is a result of pinched wires or shorted connections.

Electrical shorts refer to when current flows in the wrong path, causing a low resistance connection between the two conductors. 

Also, a break in a wire or two could cause intermittent power and signals, causing your car’s electronic system to malfunction.

In addition,  an electrical short could cause electrical drains to the car battery overnight. 

Also, electrical shorts could burn out fuses and relays; extreme scenarios could result in an electrical fire.

How to Find a Broken Wire in an Auto Wiring Harness

Testing the continuity and voltage of your wiring harness helps identify any broken and damaged circuits. And all you need is a multimeter.


Caption: Multimeter

Testing Voltage

If there is a broken wire or loose or shorted connections, the electrical components won’t get the right voltage. A voltage drop from 12 V to 0 V is an indicator that there’s a problem with your wiring harness. Follow the steps below to test your voltage.

  • First, identify the shared points using your manual.
  • Check your fuse to ensure it’s working properly.
  • Next, expose the damaged part by carefully taking off the interior rim. 
  • Ensure you expose the wires.
  • Determine the corroded and broken points on the wire.
  • Turn on your multimeter and set it to volts. 
  • Test the multimeter by touching the two probes together. If you hear a beeping sound, it functions just fine.
  • Touch the black (negative) probe to the ground and the red (positive ) probe to the malfunctioning component or a connected wire. 
  • If you notice the voltage drop is from 12 V to 0 V, you likely have a short or open circuit in the wiring system.

In some cases, the ground could cause a voltage drop. 

To prevent this, try fixing loose connections, scraping dirt, and inspecting for any corrosion on your ground bolt. 

If you still have a voltage drop, you probably have a problem with your wiring harness.

Testing Continuity

By measuring the resistance, a continuity test determines if your wire has a continuous electrical path. If you get an Ohms value over 1.0, there’s probably a lack of continuity in your electrical conductor. Follow the steps below to perform a continuity test.

  • First, make sure to switch the settings on your multimeter to Ohms.
  • Identify your sliced, corroded, or rusty wire.
  • Use a pair of pliers to disconnect the wires from the accessories on both ends.
  • Now, connect the two probes to the wire terminals. Ensure to remove the insulation coating on the wire terminals.
  • Check the reading on the multimeter. Any value over 1.0 Ohms is an indication of an inconsistent electrical path. However, the wiring harness is okay if the readings are below 1.0 ohms.

Multimeter Reading Keeps Jumping; What to do?

When testing your wiring harness using a multimeter, the readings might fluctuate or jump, indicating a power supply interruption or faulty connection.

To rectify the problem, check your connections at both ends of the wiring harness to ensure no disconnected or loose connections.

Also, check if any breaks in your insulation might be causing short circuits. 

If every connection is secure and the readings don’t change, some interference from nearby devices could disrupt the system’s electrical current flow. 

Try separating the two by moving them away from each other to see if there’s a change in the reading’s stability.

If you are still having trouble stabilizing your readings, it’s best to have a professional look and fix any necessary problems in the wiring harness.

Pros and Cons of Multimeter Tests

Using a multimeter to test your wiring harness has its advantages and disadvantages.


  • It’s cost-effective, especially when testing systems with multiple components or systems with complex wiring, since it identifies any loose connections or damaged parts.
  • Also, a  multimeter requires minimal expertise to operate and provides instant results. All you have to do is follow the necessary precautions and make a proper connection.


  • Using a multimeter requires actual contact with your components to get an accurate reading, which could prove challenging, especially if you’re handling small-sized components like connectors and wires. 
  • Since the test doesn’t perform a physical inspection on the wiring, it’s not impossible for some problems to go unnoticed. 


As previously mentioned, wiring harness connections are bound to break or fail. 

Therefore, it’s best to frequently check on the condition of your wiring harness to stay on the safe side. 

Using a multimeter to test your auto wiring harness can provide fast and accurate results. 

However, remember that this shouldn’t make you overlook the importance of a proper visual inspection of components in your circuit. 

If you have any further queries, please contact Cloom Tech.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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