What is a Car Stereo Dimmer and Illumination Wire? (Explained)

Car stereo wiring can be quite complicated to understand, especially without an owner’s manual due to the different types, functions, and colors of the wiring.

Depending on the aftermarket stereo you might have a dimmer and/or illumination wire. Some stereos will only have one of them while others can have both.

Here’s what a Car Stereo Dimmer and Illumination Wire is

Generally, a color-coded orange wire (or orange with a white strip) coming out of the stereo harness is the dimmer and/or illumination wire. They can be connected directly to the car’s electrical system and are used to control the stereo screen brightness. The wires are an important part of the car stereo because it transfers signals to the radio screen while the headlights are on but are not mandatory.

Car audio stereo wire harness lead ISO head unit
Car audio stereo wire harness lead ISO head unit

The dimmer and/or illumination wire’s function is governed by whether or not the car’s headlights are on.

They are however not mandatory for normal stereo operations and can be left disconnected.

Let’s dive into this wiring system and understand how it works in-depth.


What are Dimmer and Illumination Wires?

Dimmer and/or Illumination wires are orange, or reddish-brown colored wires coming out of the harness of your car’s stereo that is used to dim the stereo’s screen light and control the amount of brightness. 

The dimmer and/or illumination wires are attached directly to the car’s lighting or electrical system, thereby, it receives direct signals from the car’s headlights when they are turned on or off, and transfers them to the stereo.

They play an important role in ensuring the safety of drivers since more than 40% of road accidents happen at nighttime.

Dimmer and/or Illumination wires can be real life-savers by preventing unnecessary distractions due to sharp stereo unit lighting.

What are Dimmer and Illumination Wires Used For?

Simply put, the orange-colored dimmer and/or illumination wire is used to control the brightness of the LED screen light on the car stereo’s front panel. 

The dimmer and/or illumination wire, connected to your car stereo cluster, is used to dim the screen on the aftermarket car stereo.

It sends positive or negative triggers to the system to turn the headlights on or off. It’s a good safety measure because it protects your eyes from the bright light of the car stereo screen while driving at night.

But how does the process work?

The dimmer and illumination wire acts as a carrier, transferring the signal from the car’s headlight switch through the wiring harness attached to the stereo system.

An internal circuit is activated within the car stereo system when the headlight switch is turned on, thereby controlling the amount of screen brightness. Turning the headlights off will switch off the power from the dimmer and/or illumination wire and allow full-screen brightness.

Some car stereo systems have day and night-specific dimmer and/or illumination wires, which are separate from each other. At sundown, the system automatically switches to night mode, enabling you to see clearly at night.

The dimmer or illumination wire does not affect the car stereo sounds at all. Your stereo system will work even without connecting the illumination wire, but then you wouldn’t be able to control the lights. 

What is the Difference Between Dimmer and Illumination Wires?

Double din Kenwood head unit with a touchscreen display showing menu options
Double din Kenwood head unit with a touchscreen display showing menu options

Illuminator wires and dimmer wires have similar functions. Their difference lies in their voltage capacities.

The dimmer wire will take a variable 0-12V DC when headlights are on, whereas the illumination wire will take a constant 12V DC. This will also depend on the brightness of the headlight. The dimmer wire is usually orange with a white strip while the illumination wire is orange in color.

Dimmer wires are more common in modern cars, and they allow the car radio to dim to varying brightness along with the indicator lights. Read here about the instrument panel switch that controls the brightness of the instrument cluster in modern cars.

Both dimmer and/or illumination wires will dim the radio as soon as the headlights are turned on so that you don’t have a bright monitor shining in your face as you’re driving at night. 

How to Identify and Connect a Dimmer and Illumination Wire?

When you install a new car stereo, it does not come with the dimmer and/or illumination wire attached. You need to connect it yourself.  

It is quite easy to use the illumination circuit in a vehicle.

First, you need to verify whether you have a connection for that option on your factory radio harness. Clip your aftermarket harness to your factory harness to find the dimmer and/or illumination wire. 

Below is a complete breakdown of the steps involved.

Step 1

Start by disconnecting the negative battery terminal under the car’s hood by using a socket wrench and a correct insert.

Step 2

Check the back of your car head unit and locate orange-colored wires from among the different wires on the wiring harness. This is the dimmer and/or illumination wire.

In some models, this might even be a reddish-brown colored wire.

The dimmer and/or illumination wire may or may not have white stripes. Refer to the radio manual to confirm the color code or see the small label attached to it.

You can do a simple test using a bulb or voltmeter to make sure you’ve got the correct wire. Connect one probe to the tested wire and another to the car chassis.

When touching a probe to the illumination wire, you will see the voltmeter display show a variable 0-12V or constant 12V. That’s how you know you’ve spotted the right wire. 

Step 3

Now look for a brown wire coming from the car’s dashboard. The brown wire is what is controlled by the car’s electrical system that sends and is responsible for sending out the signals to control screen brightness.

Check if there are two wires one for dimmer and another for illumination.

Step 4

Next, you would want to remove the 0.5-1 inch insulation cover from the flying ends of both the wires and connect them together by soldering them and using heat-shrink tubing.

You can also secure them together by crimping them. Insert the two wires by squeezing them into opposite ends of a 16-gauge crimp connector and crimp them together. 

Step 5

After the harness wiring is finished, reconnect the negative battery terminal.

Step 6

Test it out by keying your car’s ignition and switching the lights on. If the connection is correct, you will notice the car stereo illumination dimming when the lights are on, and returning to full brightness when the lights are off.

Is it Optional to Connect the Dimmer and Illumination Wire?

Yes, connecting the illumination wire is entirely optional.

The illumination wires do not play any role in the actual sound of the car stereo system and make no difference to the proper stereo operation.

It is therefore not mandatory to connect, and many users and installers choose to leave it unhooked. This means that the screen brightness will be on maximum brightness display. 

What is the Voltage on the Car Stereo Dimmer and Illumination Wire?

The voltage on the car stereo’s dimmer wire is a variable 0-12v and the illumination wire is 12V, which is supplied by the car electronics of the car while the engine is still running.

The dimmer and illumination wire transfer signal to the car stereo as soon as the car’s headlights are switched on, which automatically dims the display screen. 


Though not mandatory to use, dimmer and illumination wires are important to the car stereo to turn the screen brightness on and off.

The signal travels through the car’s headlight switch through the wire harness, and finally to the dimmer and illumination wire, which is attached to the car stereo.

Driving at night with bright stereo lights can be hazardous. Dimmer and/or Illumination wires help control the brightness and thereby prevent any unnecessary accidents.


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