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HomeTips & GuidesAutomotive Wiring Harness Signal Wire: Signal Types, Design Challenges, and Future Trends

Automotive Wiring Harness Signal Wire: Signal Types, Design Challenges, and Future Trends

Automotive wiring harness signal wire forms half or a third of the cables in wire harnesses, the others being power and ground cables. 

These wires can transmit different voltage signals depending on the connected electrical component.

Regardless of these differences, the wires should be highly reliable and adhere to standardized formats like color coding. 

Here’s all you need to know about these wires, including the types of signals they carry. Read on to learn more!

Table of Contents

What Are Automotive Wiring Harness Signal Wires?

Signal wires in car wire harnesses are conductors that transmit analog or digital electrical signals between vehicle components. Some of these analog and digital signals include the following.

Sensor Signals

Vehicles have multiple sensors to check engine and transmission operations and for safety systems. 

The harnesses connecting these sensors to the modules or control units must have signal wires to send the digital or analog signals for processing.

A mass-airflow sensor signal wire harness

A mass-airflow sensor signal wire harness

Audio Signals

Car head units transmit audio signals to speakers via signal wires in the harnesses. These color-coded cables send the power to the positive and negative speaker terminals.

A car stereo wire harness, some being audio signal wires

A car stereo wire harness, some being audio signal wires

Communication Bus Signals

Modern vehicles with control units to run and monitor various vehicle systems must have buses to communicate. Most use the two-wire CAN bus to exchange data between the modules.

Engine control unit with its signal and power wires

Engine control unit with its signal and power wires

Instrument Cluster Signals

The instrument cluster houses various gauges, such as the tachometer, speedometer, engine/coolant temperature, and fuel level gauges. Data from the sensors gets to these gauges using signal wires via the respective modules.

A car’s instrument cluster with multiple gauges

A car’s instrument cluster with multiple gauges

Control Signals

These signal wires transmit electrical current to various electronic components to control their operations. Think of devices like windshield wipers, headlights, power mirror adjustment, power windows, etc.

Importance of Color Coding Automotive Wiring Harness Signal Wires

Signal wires are critical in vehicle electrical systems, and color coding them is equally vital for the following reasons.


Some wire harnesses, such as for the car stereo, contain numerous wires to serve different functions. 

Color coding makes it easier to identify the functions of these wires when connecting or maintaining them to minimize errors.

Color-coded car stereo wires

Color-coded car stereo wires


Color coding enables standardization when dealing with multiple manufacturers. 

On a global scale, these international automotive industry standards allow compatibility and interoperability between devices and cars made by different manufacturers.

From a technician’s point of view, standardization simplifies maintenance and new installations, such as when upgrading stereos.


By enabling accurate interconnections, color coding reduces the risks of shorting or ground faults that can damage the components or circuits.

Quick Troubleshooting

If electrical issues arise on the connected end devices, you can troubleshoot the problem quickly by following the color-coded wire. Or, you can check the signal wire’s color and find its connection at the source.

These conveniences make it easy to isolate the problem for diagnosis and cut downtimes.

Easier Documentation

Lastly, color coding signal wires make it easy to read and document wiring diagrams. You can even follow these circuit diagrams and repair or replace the components as DIY projects because it is easy to identify the function of each cable.

A car wiring diagram

A car wiring diagram

Challenges When Designing and Making Car Signal Wires

Automotive cable harness signal wires must be highly reliable. So, you must think about these challenges when designing and manufacturing them.

Temperature Extremes

Areas in the engine bay and around the transmission can become hot when the vehicle moves.

 These conditions expose signal wires in those areas to extreme temperatures, which can burn their insulation or reduce electrical conductivity.

So, you must design the wires to have insulations that can withstand high temperatures or use heat shielding materials like corrugated tubes.

Car wiring harnesses in corrugated tubes

Car wiring harnesses in corrugated tubes


Exposure to moisture and other corrosive liquids can eat away the insulation, exposing the wires to short-circuiting. 

This exposure will interfere with signal transmission, causing potential safety risks like electrical fires when driving.

The solution is to use seals on the electrical connections and secure the conductors using waterproof/corrosion-proof materials.

Vibrations and Mechanical Stress

Car movement causes vibrations on electrical wires, particularly around their electrical joints, leading to failure, wear, or disconnection.

Implement strain relief features like grommets and clips to mitigate these issues by firmly securing the cables. Secure mounting prevents abrasion among the wires, as well.

Also, include locking mechanisms in the joints to handle the mechanical stress.

Electromagnetic Interference

Electromagnetic noise can interfere with signal integrity, making the components receive erroneous data. Therefore, you should install shielding materials in the insulation to block the EMI.

This shielding should go hand-in-hand with proper grounding to channel interference away from sensitive electronics.

Higher Data Transfer Rates

The increasing vehicle control modules, sensors, and connectivity necessitate high-speed data networks to handle real-time data transmission. 

Therefore, the signal wires should support increased bandwidth to accommodate advanced systems like autonomous driving.

Some of these cables might switch from copper wires to fiber optic, which transmits light signals with almost zero interference.

Fiber-optic wires

Fiber-optic wires

Intelligent Wiring

Signal wires are already becoming intelligent enough to enable seamless communication between control units and sensors. 

So, they will only become better, especially when connecting adaptive vehicle systems.

Power over Data Line (PoDL)

Wire harnesses contribute significantly to the vehicle’s weight and will become heavier as cars advance.

 Integrating electrical power and signal lines into the same line reduces the copper footprint in each auto, making it lighter.

This system is similar to Power over Ethernet in cabled internet connections to antenna dishes.

Power over Ethernet adapters

Power over Ethernet adapters

Alternatively, car manufacturers can use lighter wire harness materials like aluminum and glass (fiber optic).

Enhanced Shielding

Electromagnetic noise is a significant factor when using metal wires. And as electronics increase in vehicles, EMI will only increase. 

Therefore, enhanced shielding is necessary to block this increased noise.

More Standardization

Modern vehicles will likely have standardized communication protocols extending to the hardware level (signal wires). 

Whether fiber optic or metal wires, signal cables might be standard in all vehicles to enable cross-platform communication and integration.

Wrap Up

As you can see, signal wires are crucial components in car wire harnesses, so you should design them correctly, including using standardized color codes.

But as vehicles advance technologically, keep an eye on the future trends to keep you up to date. 

And keep note of the design and manufacturing challenges to ensure the signal wires meet their operating requirements. We can help you get reliable automotive signal wires for your project. Contact us, and we’ll point you in the right direction.

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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