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HomeTips & GuidesCar Audio Hi/Low Input Wire Harness: Functions, Components, and Installation Steps

Car Audio Hi/Low Input Wire Harness: Functions, Components, and Installation Steps

This article explains how a car audio hi/low input wire harness can enhance your vehicle’s sound quality.

You might want to upgrade your car’s sound system to have more bass without replacing the factory radio. Maybe you like the look of the radio, or it gives you control over most of the vehicle’s functions.

However, linking the stereo directly to a subwoofer is impossible because most stock units don’t have RCA pre-outs. Here’s how to set up a car audio hi/low input wire harness to create an interface for enhancing the sound system.

Table of Contents

What Is a Car Audio Hi/Low Input Wire Harness?

This audio wire harness primarily consists of a high-to-low level or line-output converter to create the connection interface. Either of these devices sits between the speaker wires from the car factory radio to an aftermarket amplifier to help inject bass into your vehicle.

Therefore, the function of the hi/low input wire harness is to convert high-level audio signals to low/preamp levels. 

The high levels come from the factory car head unit, and the low levels go into the amplifier.

External aftermarket amplifiers require these low-level signals to power subwoofers and speakers.

Functions of a Car Audio Hi/Low Input Wire Harness

This wiring harness has the following functions.

Signal Conversion

The primary task of this cable assembly is to convert the speaker-level signal outputs that power the car speakers into low-level signals. 

Connecting amplifiers directly to the high speaker-level input signals will result in a distorted sound output. 

However, low-level signals from the converters are clean, clear, and more consistent, meaning the amplifier will emit better sound-quality signals.


These harnesses can work with various stereos from different car makes and models, creating a standardized interface for hooking up any amplifier you’d like.


Some hi/low audio wire harness converters have adjustment features like gain control for fine-tuning the output signal to integrate better with the amplifier.

A gain control adjustment knob

A gain control adjustment knob

Not only is this feature good for integration, but it also ensures amplifiers perform at their optimal levels. They should output high-quality bass signals with zero distortion.

Signal Isolation

Some of these audio harnesses feature isolation circuitry that minimizes or eliminates the risk of signal interference from exterior electromagnetic frequencies.

Components of a Car Audio Hi/Low Input Wire Harness

This wire harness has the following parts.

Input/Output Wires

Input wires connect to the stock stereo’s speaker wires to channel in the high-level signals. On the other hand, output wires transmit the low-level audio signals from the converter to the amplifier.

A vehicle’s sound system upgrade components

A vehicle’s sound system upgrade components

Power and Ground Wire

The signal converter might need a power supply input to run its internal circuitry.

 It may also need a ground wire to link the harness to the chassis to channel noise frequencies away from the audio signal.

Remote Turn-On Wire

This wire links the head unit to the external amplifier to turn it on when the stereo powers up after turning on the ignition switch. 

It is a critical part of the harness because it ensures the amplifier only turns on when the stereo is on to prevent battery drain.


These components link all the wires to their corresponding terminals along the harness. 

For instance, the harness must have RCA cable connections for the wire outputting the signal from the converter to the amplifier.

A car amplifier cable with RCA connectors

A car amplifier cable with RCA connectors

Signal Converter

A signal converter is the most critical feature in this harness because it handles the high-level to low-level signal conversion. Depending on your budget, you can purchase either of these types of converters.

Hi-Low Converter (Low-Cost Option)

This converter is rather basic. It taps into the speaker wires and channels the signals via RCA outputs. 

The device is affordable but does not deliver the same sound quality you’d get when using an aftermarket head unit with RCA pre-outs.

Therefore, the unit is ideal for those on a budget or those who don’t have a meticulous ear.

Line Output Converter (High-Cost Option)

If upgrading your sound system, you would appreciate the audio signal quality from a line output converter.

This device converts actual signal because it taps into the high-level speaker wires and drops the signal. 

The drop-down delivers the signal required by the amplifier without interfering with the fidelity from the source.

We recommend using this converter because it will give you the best bass and audio quality.

Adjustment Controls

Line-out converters usually feature knobs for level and gain adjustment to fine-tune the output signal to match the amplifier, subwoofer, and speaker requirements.

Multicolored car radio wires

Multicolored car radio wires

Noise Filters and Reduction Circuitry

Noise reduction components minimize or cut off interference from the input and output wires to maintain audio fidelity.


Fuses safeguard the harness and converter from damage caused by voltage spikes, shorting, and other electrical faults.

Protective Casing

Lastly, the harness has an enclosure to protect the wires and other components from external factors and physical damage.

Benefits of a Car Audio Hi/Low Input Wire Harness

  • Universal compatibility/integration
  • Better sound quality
  • Signal protection from interference/electromagnetic noise
  • Preserves the factory radio look and functionality
  • Easy to install
  • Adjustable gain and level controls

How To Install a Car Audio Hi/Low Input Wire Harness

You’ll need these items to complete this installation.

  • Hi/low car audio input wire harness
  • Wire stripper
  • Screwdriver
  • Wire crimping tool
  • Pliers
  • Crimp connectors or soldering tool
  • Electrical tape or heat-shrink tubing
  • Your vehicle’s electrical wiring diagram
A car audio specialist holding the items for upgrading a vehicle’s sound system

A car audio specialist holding the items for upgrading a vehicle’s sound system

Step 1: Disconnect the Battery

Before getting into the exciting part of the project, disconnect the negative terminal from the battery.

Step 2: Access the Speaker Wires From the Factory Radio

Remove the trim panels around the factory head unit and locate the speaker wires. You might have to unscrew the stereo to reach these wires.

Step 3: Identify the Speaker Wires

Use your vehicle’s wiring diagram to identify the front and rear speakers wires from the radio.

Step 4: Tap These Speaker Wires

Use the wire stripper to remove a tiny insulation section from the speaker wires and do the same on the hi/low wire harness’s input wire.

A vehicle’s audio player wire harness

A vehicle’s audio player wire harness

Install connectors on the speaker wires to tap the sound signal. Mount the corresponding input wire to these speaker wire connectors and crimp them to form a solid joint.

Step 5: Connect the Power and Ground Wires

Harnesses with line-out converters usually have power wires. Connect this line to a constant 12V power source at the fuse box. You can mount the system’s fuse at this point or install an inline fuse to protect the converter.

While at it, link the system’s ground wire to an unpainted surface on the vehicle’s chassis and apply dielectric grease.

Step 6: Connect the Remote Turn-On Cable

Connect the remote turn-on cable (usually a blue wire) to the similar-function wire from the head unit or ignition-switched power source to the amplifier.

Step 7: Connect the Output Wires

Link the output wires from the harness to the amplifier using RCA connectors. The speakers come after the amplifier. Link them, as well.

A car amplifier

A car amplifier

Step 8: Organize and Secure All the Wires

Organize the wires in the vehicle to minimize interference, then secure them using cable clips or zip ties. 

Ensure you test the setup before reinstalling the trim panels. 

But you can install the head unit in its slot if you have removed it to access the wires.

Step 9: Test the Sound System

Reconnect the negative battery terminal, then test the audio system. Adjust the gain and level controls on the harness converter to match the amplifier’s input. 

After that, fine-tune the system using the head unit and amplifier audio settings to achieve the best sound quality.

A car electrician linking connectors for powering a stereo in a vehicle

A car electrician linking connectors for powering a stereo in a vehicle

Step 10: Reinstall the Dashboard Panels

Once everything is in place, refit the dashboard trim panels, and that’s it.

Wrap Up

Modern vehicles come with sophisticated head units that you cannot do without. Therefore, the only way to go if upgrading your sound system is to use a hi/low input wire harness. And we recommend one with a line-out converter to get the best sound quality.

You can do this upgrade as a DIY project, and we can ship the harness to your location at a reasonable cost. Contact us or comment below to let us know your specifications.

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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