What Is The 12V Accessory Wire On A Car Stereo?

The car stereo is part of what makes driving fun as it keeps you entertained and informed as you drive. This system comprises different parts connected by different wires. If these wires are not connected properly, the car stereo won’t work.  

This is why one should recognize each wire in this system, so you know which goes to which. One of these wires is the 12V accessory wire. So what is the 12V accessory wire on a car stereo?

This article explains what the 12V wire is and how to identify it.

The 12V accessory wire on a car stereo

The 12V accessory wire is one of the three power wires a car stereo utilizes. It is red in color and helps trigger the stereo to come on. However, for this wire to turn on the stereo, your ignition key must be in the accessory position.

What is the mechanism here?

The 12V accessory wire is connected from the stereo to the ignition switch accessory wires. So when you turn on the ignition, it activates the 12V accessory wire to turn on the stereo. This means that the 12V wire must stay connected to power the stereo. 

Taking the key off the ignition automatically causes the accessory wire to lose power. Once power is withdrawn, the wire shuts down and enters low power mode. No power on the accessory wire, no stereo coming on. The next question will be, how does one identify this wire?

How to identify the 12V accessory wire

Aside from knowing that the accessory wire is red, here is a simple way to identify the 12V accessory wire.

Cars with factory or OEM stereo

  • Set your multimeter to 12V (test light is also an option)
  • Ensure the ground side of your multimeter is secured in the dash
  • Take out the radio to access the wires behind
  • Turn the ignition to ACC, examine and test all the wires
  • One wire should carry 12 volts
  • Turn off the ignition; this should take away the volts
  • Turn the key to ACC again. If the voltages return, then this is the 12V accessory wire. The accessory wire functions only when the ignition is on and loses power when the ignition is off.

Cars with an aftermarket stereo

  • Set your multimeter to 12V ( you can also use a test light)
  • You will either do this test at the fuse box or ignition harness
  • Ensure the ground side of the tester is secured in the dash
  • Turn on the ignition, examine and test all wires in the ignition harness or fuse box
  • One of the wires should read 12 volts
  • Turn off the ignition; the voltage should disappear
  • Turn on the ignition again. If the voltage returns, then it is the accessory wire.

Alternatively, you can watch the helpful video below, which explains the process.

What wire powers the stereo system?

Typically, two or three wires are used to power the stereo system, depending on your car. 

  • The yellow 12V constant wire functions to keep the memory alive and powers the clock, presets, etc. It’s always hot because it works whether the car is on or off yet retains its 12-volts. 

 

  • Next is the red 12V accessory wire (labeled ACC). It helps turn on the stereo and works only when the ignition is on or when the car is running. 

 

  • The third wire (if available) is the dimmer or illumination wire. It comes in orange mixed with white stripes and helps power the headlights and dash lights. It is this wire that makes these lights dim or shine brighter.

 

Conclusion

Over 18 wires are used during car stereo installation; amongst is the 12V accessory wire. So what is the 12V accessory wire on a car stereo? The red-colored wire features as one of the wires that power the stereo. Its major function is to turn on the car stereo. 

But must be connected to the ignition switch wire. So when you turn on the ignition, it receives power to turn on the stereo. One way to identify the 12V wire is to test with a multimeter or test light. If it shows 12 volts with the ignition on and 0 volts with the ignition off, it’s the accessory wire.

Suppose you enjoyed this article and are looking to tinker with your car stereo but wonder if it would void your car’s warranty. We have a whole article around will an aftermarket stereo void warranty.

Alex
Alex

I loved my car but was frustrated with my media system. So I upgraded my stereo, making silly wires and precarious phone mounts a thing of the past. The Apple Car Play stereo was so good I wanted to show more people how this could be done and truly upgrade their cars multimedia system!

Founder
StereoUpgrade.com

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