12V Accessory Wire On A Car Stereo – What Does It Do

Are you confused about accessory wire on a car stereo? I’ve been there.


If you have ever driven a car, you’ve noticed wires in the car’s interior. There’s usually a wire going from a plug behind the steering wheel to the stereo. This is known as a 12-volt (12V) accessory wire.

A car stereo, really any car audio system, requires power to work correctly. There are many different types of power requirements; however, this article will focus on voltage. 12v accessory wire has a lot of benefits, which makes it ideal for some applications.

How Do You Know If You Have A 12V Accessory Wire On Your Car Stereo Head Unit?

If you look at the back of your head unit, you will see a number of wires connected to the radio. If there is no connector on the radio and only bare wires coming out of it, you do not have a 12V accessory wire in place.

The other possibility is that the harness is already attached to your car stereo, and there isn’t any way to tell if it has this wire without detaching it from the back of your head unit. If you are handy with some electronics tools, here’s how you check:

  • Disconnect all connectors from your car stereo (including antenna)
  • Start at one end of the harness and disconnect each colored wire from its respective connector
  • Wrap electrical tape around each disconnected wire so they can’t touch other wires or metal inside your dashboard
  • Attach each wire to its connector again except for the blue/white wire
  • Turn on your ignition to ACC (usual power through cigarette lighter) or jump battery power directly to blue/white wire with another piece of electrical tape over it, leaving an inch sticking out.

If all works fine, use paper clips instead of electrical tape and follow the above steps until you get an error message like “No CD” or “No Audio.” At that point, start attaching every other pair until you know which one(s) is causing the error. You now know what extra functions that harness gives.

What Does The 12V Accessory Wire Do For Your Car Stereo?

The 12V accessory wire is usually a RED wire located in the vehicle’s fuse box. It’s typically found in a small harness that is taped to the back of the fuse panel or under the dash.

The 12V accessory wire on a car stereo is what you use to power your antenna, amplifier, equalizer, or any other 12V device you want to install on your car.

On a modern stereo, the accessory wire has switched power. This means that the wire only has power when the car is on and there is no need to disconnect the battery when installing.

There may be two options for a 12-volt accessory wire in some vehicles: one that only turns on when the key is in the accessory and another that turns on only when the key is in the run.

How Does It Work?

When you turn on your car, you’ll notice that some things come on immediately, like radio presets and USB power. Others will take a few seconds, like your car stereo and navigation head unit. That’s because those are controlled by an ACC (accessory) circuit. When the ACC circuit is activated, the current passes through it and starts the stereo system. This lets you listen to music while driving around town or taking care of errands with the car turned off but not running down the battery.

In addition to providing a critical safety function (allowing you to listen for traffic while driving with windows closed), this makes possible all kinds of fun customizations: adding an extra subwoofer or amp; powering an amplifier-equipped glove box, or even installing an aftermarket navigation system that runs exclusively off 12 volts when driving around town – just like OEM navigation systems do!

12V ignition wire, also known as 12V accessory or “switched” wire, is a feature found on almost all car stereos. Its purpose is to automatically turn on the car stereo when the vehicle is started and shut it off when the car is turned off. It’s not required for your stereo to work, but it does make life a lot easier. If you don’t connect it, you will have to manually turn on and off your new stereo every time you get into and out of your vehicle.

Connecting your stereo’s switched wire to your vehicle’s ignition switch involves locating this wire in your car and determining where your vehicle’s 12V switched power source is found. You can then connect these two wires using a male spade terminal connector and electrical tape. In many cases, this process can be done without cutting any wires or using any special tools.

The ACC wire is the accessory wire, and it’s responsible for turning on the stereo when you turn the key in your car. Some cars need this wire to be connected for the head unit to turn on. Other cars will require that you connect this wire in order for certain features on your stereo to work properly.

If you don’t want to connect your stereo’s ACC wire, there are some things to keep in mind.

You may not be able to control your stereo from your steering wheel controls if you don’t connect the ACC wire (depending on what brand of car stereo that you have).

12V accessory power is used to power up accessories that are not being used for driving the vehicle, such as a GPS, dashcam, etc. Accessory power can be obtained from the fuse box or a switched wire in the ignition. It’s essential to keep in mind that not all vehicles have accessory power available in the fuse box, so using an ignition wire would be necessary.

The easiest way to determine if your 12V Accessory Wire is live is to first turn your key to the “ACC” position. When you do this, you should hear a clicking sound (this is the sound of the relays and fuses in the vehicle powering up).

If you hear this clicking sound, you can ensure that your 12V Accessory Wire is live. Unfortunately, we have found that many vehicles don’t make this clicking sound, and therefore it does not necessarily mean that there is no power. Ensure all vehicle accessories are turned off before testing for power.

First, to wire an accessory relay, locate the vehicle’s fuse panel and disconnect the power wire leading from it to the stereo. Then, install the relay between the power lead and the stereo, and connect a switch that can be easily reached from the driver’s seat to one of the terminals on the relay.

How Would You Use The 12V Accessory Wire On Your Car Stereo Head Unit?

Without a 12V accessory wire, a stereo would have to turn it on manually. You would also have to do this with any other device connected to your head unit via the accessory wire.

The 12V accessory wire allows you to turn accessories on or off from the head unit itself, should you choose not to leave them powered up 24/7. When the car stereo is turned off, the amps also shut down, or a subwoofer mutes. This prevents damage or strain caused by the continuous powering of these devices while they aren’t in use.

Here are some examples of what your remote wire could be used for:

  • Turning an amplifier on or off
  • Turning a subwoofer on or off
  • Turning a navigation system on or off
  • Turning dash cameras (when not in motion)

Lastly, I would like to talk a little bit about the 12V accessory wire. The accessory wire is very important because it controls when your car stereo turns on and off. By having it connected to your ignition or fuse box, you can have your radio turn on when the key is in the ACC position, which is essentially the same thing as turning on your car.

Then, when you turn off the key in the ACC position and then again all of the ways, your radio will turn off. This is extremely handy because if you are using this device as a head unit (the main control center for an automobile audio system), then you don’t need any other parts to make sure that it works properly.

You can also use this accessory wire to power other devices, but keep in mind that it’s only a 12-volt signal so more than likely you won’t be able to run anything high powered off of this particular wire unless there are special circumstances such as running multiple wires into one with an amp or using voltage regulators.

The accessory wire can be a valuable asset to help you get more out of your audio system.

You can use this wire to power up an additional device, such as a GPS, phone charger, or rearview camera.

Another way you might use the accessory wire is by hooking up a relay that will switch on an amplifier when the vehicle is running and switch it off when it is not. Many amplifiers have a remote turn-on/off feature that lets you do this with just one wire.

The accessory wire can also be used for “anti-theft” devices that activate alarms when someone tampers with your stereo. Simply connect the alarm to the accessory wire and if anyone attempts to unplug your stereo without the passcode, they’ll set off your alarm. Just remember that any anti-theft device will drain some of your car’s battery even when it is switched off.


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