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HomeTips & GuidesNo Illumination Wire on Car Radio: Illumination Wire Basics

No Illumination Wire on Car Radio: Illumination Wire Basics

Check out this post to gain insights on how to deal with no illumination wire on car radio

The guide discusses some quick-fix solutions to this problem to ensure you continue reaping the best out of the component. 

Most importantly, this guide will elaborate on the illumination wire’s role in your car’s electronic system. 

Therefore, read on for a detailed review of the illumination wire and how to fix it if it fails. 

Table of Contents

What Is the Illumination Wire?

It’s a wire that dims the brightness of the car’s radio display screen. Primarily, it is responsible for the stereo system’s negative/positive triggers that control when the headlights turn on/off. 

The cable is essential at night when an extremely bright radio display can blind the driver, leading to an accident. Hence, it dims the radio display when the headlights are turned on, helping the driver focus on the road ahead. 

Usually, you’ll find the illumination wire on the car’s wiring harness, and it also has a link to the car’s lighting system. Also noteworthy is that it’s usually colored orange. But you may find others coded orange but with a white strip. 

How to Tell if Your Car Has an Illumination Wire or Not?

Car Radio Display. 

Car Radio Display. 

There are three main ways to identify whether your car’s illumination wire exists. Let’s look at them in detail. 

Car’s Manual

Most car user manuals will always reveal if a car features an illumination wire installed. 

However, this is not always the case, as some may fail to mention this crucial information despite the existence of the wire. 

So, if your car manual mentions that it exists, that’s enough proof. But if it says nothing about it, you may have to check it out manually. 

Check Manually

Confirm if the illumination wire exists by checking out behind the radio for the presence of an orange wire in the wire harness. If it is there, then this is the illumination wire. It’s usually orange in some cars with a white strip, so check out if you can find this one. 

Test with a Multimeter

A multimeter. 

A multimeter. 

If you can’t locate it using the above two methods, the alternative is to find it via a multimeter. 

Connect the device to the radio’s wiring and check if there’s a change in the voltage reading when you turn on the headlights. 

A voltage change indicates that the radio has an illumination wire in place. 

Why Some Cars Lack an Illumination Wire

Car Dashboard. 

Car Dashboard. 

If you find out there’s no illumination wire from the above tests, you may be left wondering what could be the reason. There are many explanations, as it depends on the manufacturer, and we’ll look at each in detail. 


The main reason for omitting the component is cost cutting. Having it comes with the burden of the extra costs that will balloon the overall cost of the car radio. So, some manufacturers opt to leave it out. 

Car Radio Design

Most modern cars have an LED display with dimming capabilities to make it easy on the eye. Such vehicles don’t require an illumination wire as the radio design means that the light can never be a distraction. 


Also, probably, the manufacturer doesn’t deem the illumination wire compatible with the FM radio. In such a case, they will omit it altogether, which could be why you don’t find it in the radio harness. 

But does this affect the working of the FM radio? Not at all. The radio will keep working normally. 

How to Solve the No Illumination Wire Issue

Car radio screen. 

Car radio screen. 

If your car’s radio doesn’t have a means of adjusting the no illumination wire issue, there’s a way out of it. You can opt for either of the three options below. 

Adjust the Screen Brightness

The car’s radio has a setting that you can use to regulate the brightness levels to your liking.

 This setting will come in handy in setting up the brightness to a limit that is bearable to your eyes and doesn’t affect your road vision. 

Switch on the Ambient Lighting

If you cannot set the radio’s screen brightness, there’s the option of adjusting the ambient interior lights to match the radio’s. 

Such a setting eliminates the apparent contrast, so you won’t strain to see the road ahead. 

Use an Aftermarket Adapter

Finally, you can install an adapter incorporating an illumination wire into the radio. 

The exercise requires some expertise, so you’ll have to involve a professional mechanic for an excellent fix.

Illumination Wire vs Illumination Dimmer: Are They Similar?

Car radio with an LED Display.

Car radio with an LED Display.

How about using an illumination dimmer in place of an illumination wire? Are they similar components? 

As stated earlier, the illumination wire links the car’s radio and the lighting system. 

Hence, the car radio can regulate its lighting depending on whether the headlights are switched on. 

On the other hand, an illumination dimmer is a manual switch, typically a knob you use to regulate the radio’s brightness. 

So, the big question is if you can replace an illumination dimmer with an illumination wire. 

It all depends on the making of the car’s radio system. If the radio features a functionality allowing you to dim the display manually, it’s possible to replace the dimmer with an illumination wire. 

Benefits of an Illumination Dimmer Over Illumination Wire

Here’s why you should opt for an illumination dimmer over an illumination wire. 

  • If you leave your headlights on, the illumination dimmer will automatically turn them off. Hence, it saves you from the inconvenience of switching them off manually. 
  • A dimmer also comes in handy in customizing the level of brightness you want for the car’s interior. 
  • It adjusts the degree of brightness automatically depending on the ambient light. Therefore, you don’t have to worry about driving on a road with other motorists fully switching their lights. 
  • An illumination dimmer ensures you have the light intensity you only require, so it helps you save money. 

Limitations of a Radio without an Illumination Wire

Driving at night. 

Driving at night. 

What are the challenges you face when your radio lacks an illumination wire? Let’s explore them below. 

Limited Visibility

You cannot comfortably access the radio screen as there are no means of adjusting the brightness per the ambient light conditions. 

Thus, you can not use functionalities such as volume control, frequency settings, and other critical info. 

The problem would be more pronounced in low light conditions.

More Distractions

Think of a scenario when you’re trying to read a blurry car display while driving. 

You may cause an accident as all your attention will be drawn towards the radio. 

It is a cardinal problem with a radio without a working illumination wire, especially in low-light conditions. 

Incompatibility with Some Autos

Some car models require the illumination wire to work efficiently for the radio. 

If it is faulty, you may require an overhaul of the entire unit for the radio to function. 

Nonetheless, some cars do not require the illumination wire to function. 

Hence, some car owners remove it entirely in such vehicles for maximum brightness of the radio display. 

How to Connect the Radio Illumination Wire?

The car electrician connects the radio to the car. 

The car electrician connects the radio to the car. 

  • First, disconnect the negative battery terminal. This step will ensure you don’t experience electric shock. 
  • Next, find the car’s illumination dimmer wire from the back of the stereo system. It is usually coded orange but could be reddish-brown in others or orange with a white strip. If you’re unsure if it’s the one, your car’s user manual should come in handy in helping identify it. Also, some cables feature an indicator tag, which should easily help you identify the illumination wire. 
  • Connect the aftermarket illumination wire adapter to the wire you’ve identified. You should be careful at this step to ensure that the wires match so that you get the connection right. 
  • Using a wire stripper, remove the cover from each cable. Then, insert a 16-gauge crimp connector on either side of the stripped wires and connect the two. Next, connect the other matching cables in the wire harness and reconnect the negative terminal. 
  • Test if your connections are okay by switching the aftermarket car stereo on and then the headlight switch. Note if the radio lights dim when you turn on the headlights and return to normal brightness when you switch off the headlights. This step should confirm that the illumination wire connection is perfect. 


We can regard the radio illumination wire as a safety component primarily due to its role in helping you focus on the road ahead. Hence, you should ask your mechanic to fix it if it is dysfunctional. 

But some cars lack it because they have coping measures such as dimmable LED lights that adjust according to ambient brightness. 

Therefore, the bottom line is to investigate if it is a critical part of your car or whether you can do without it. 

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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