How to Install A Car Stereo Without A Wiring Harness Adapter

Learning how to install a car stereo without a wiring harness adapter is very strait forward if you have the proper tools handy for the job! Your main goal is to install a new stereo into your vehicle while not damaging important wires or causing any automotive fires in the process.

I’ve decided to create a step by step guide for this, it will be pretty quick and easy to understand hopefully. Ill list the tools that I recommend having handy for this job below as well.

When Should You Use An Aftermarket Harness Instead Of Your Factory Harness?

Before Removing your stereo a good idea would be to take a look at your wiring diagram. Particularly, take a look at to see if you have a wire named “Accessory (Acc)” or “12v Switched”.

If you do not, this generally means that you would require a harness. But not just any type of harness, youll need a harness with a data bus module. A Data bus module is used when the vehicle uses data to turn the stereo on and off instead of a normal 12 volt.

Data bus driven signals send a series of data through a low voltage signal. A Data bus module receives this signal and turns it into a 12v signal to turn on your aftermarket radio.

What Tools Do you Need for this job?

You’ll need a couple of tools before you get started, hopefully you have them already. Ill only list the important tools for you, i’ll assume you already have a drill with the drill bits needed to remove/install your new stereo.

Step 1 – Do The Proper Research

Please have a printed wiring diagram for your vehicle before starting work. One on the computer or saved to your phone can also be used as well.

Before you start, do some research on the type of audio system that you have. You need to know what your dealing with before you start. Do you have a premium audio system with an amplifier? Do you want to retain any factory features that your old stereo had?

Generally, your factory stereo works with your factory bluetooth, aux input, usb input etc. Keep this in mind when you decide to replace it, the good part is that your new stereo could have some of these functions if you purchase one with them.

Aftermarket stereo harnesses sometimes help to retain factory features like amplifier’s, steering wheel controls and a few other things. They use data modules on the harness to retain these features, not having harnesses like these can definitely make it difficult.

Step 2 – Identifying Your Wires

With your multimeter and wiring diagram handy you can start to find your wires and verify they match to the diagram. The only connections you need are:

  • Your speaker wires
  • Power wire
  • Accessory wire
  • Ground Wire
  • Amp turn on or power antenna lead

Note that If your vehicle has an amplifier that uses fiber optics or only uses 2 channels (only 2 sets wires) for amplifier input you need to perform an amplifier bypass.

Step 3 – Making your connections

Making your connections is the fun part. You’ll need your wiring diagram handy with you while you while you make your connections to verify you are connecting your new radio’s harness to the right wires on your factory harness.

In this example we’ll use a standard aftermarket radio harness (Single Din). You’ll be able to follow along if your installing a single din stereo, a double din will have a few more wires that will require additional connections outside of the factory harness.

These wires below are what youll most likely find on your new aftermarket harness. All youll need to do is to match them up with your factory wires using your wiring diagram.

After you use your multimeter to verify power, ground and Acc you can start to make the connections using your wiring diagram. What your doing here is matching your vehicles wires to the harness that came with your new stereo. Make sure that you cut your wires one by one. When all the wires are cut you can now strip them about a half of an inch back and start to make your connections one at a time using your crimping tools and crimping caps.

Image credit goes to the good people at LifeWire.com
  • Yellow – Wire dedicated to a constant 12 volt on your factory side.
  • Red – Is dedicated to a switched power source. This source receives power only when the key is turned to the accessory position (The position right before you start the car).
  • Black – Is dedicated to a negative ground for your vehicle. Sometimes your factory system does not have a wire for ground, in this case youll have to ground the black wire on the new stereos harness.
  • Blue – Power antenna lead used to power an amplified antenna or a powered antenna. If this is present on your wiring diagram you’ll need to connect to this or your am/fm signal will be terrible.
  • Blue w/ white – Amplifier turn on. Is used to turn on your factory amplifier if it can be integrated with per your new stereo. If your factory amplifier does not use a low level input this will be an easy task.
  • Purple & Purple w/Black – Are dedicated to your rear right speakers. Solid purple being right rear speaker (+) and purple w/ Black being Right Rear speaker (-).
  • Green & Green w/black – Rear right speaker (+) and Rear right speaker (-).
  • Grey & Grey w/ black – Right front speaker (+) and Right front speaker (-).
  • White & White w/ black – Front left speaker (+) and front left speaker (-).

Frequently asked Questions

How do I test my speakers before making my connection?

Use a speaker popper or a 9 volt battery. A speaker popper will require you to connect to the – and + of the speaker wire and press a button on the popper to move the speaker. If you hear a pop noise you have the right wires. Verify polarity with the same popper by watching the LED light up in the area on the popper that signifies proper polarity.

Where can I find the wire diagram?

Crutchfield offers them when you purchase the audio equipment from them. Of course they charge for this diagram.

How do I find out how to remove my radio?

If you order a metra or scoche branded dashkit you will receive the instructions in your packaging.

What if my car has a factory amplifier?

Consult with your local car audio shop to avoid any wiring mishaps.