Install a New Head Unit

Install a New Head Unit

After you've pulled out your head unit, you may want a few tips on putting in a new one.

Most technophiles' needs will exceed the capabilities of their factory car stereos very quickly. First, they'll want to play some computer-based audio format, such as MP3, and they'll have to use a tape adapter to get it into the stereo. Then they'll start wanting to load up MP3s on a CD, and they'll be frustrated that the built-in stereo won't play them. Even if it does, they'll expect the worksintuitive navigation, album art display, and track names. They may also want to install satellite radio in addition to the CD changer. With a three-to-five-year development cycle for new products, auto manufacturers usually can't keep up. That's where the aftermarket comes in.

If you're looking to hook up an in-car computer to your factory stereo, there are definitely ways to do it, but it's often easier to just upgrade to an aftermarket stereo with auxiliary inputs, or even a fold-out video screen. And as you may want to upgrade your sound in the process, adding an external amplifier [Hack #15] is a very standard and beneficial upgrade. But if you're just replacing the head unit, in many cases it is simply a matter of splicing together the correct wires.

Standard Head Unit Wiring

A bundle of wires grouped together in a car is called a harness. All radios with built-in amplifiers have pretty much the same wires going from their specific harness to the car, with a different plastic end connector.

Your conventional factory and aftermarket head units usually have the following wires (see Figure):

  • Front left speaker (two wires, + and)

  • Front right speaker (two wires, + and)

  • Rear left speaker (two wires, + and)

  • Rear right speaker (two wires, + and)

  • +12V switched power (usually red)

  • Ground (0V, usually black)

  • +12V standby power (usually yellow)

  • +12V cable out (indicates radio on; goes to amps and retractable antennas)

Since these wires are usually present in any car, installing another head unit is often as simple as buying the right adapter to link your new head unit to the corresponding wires of your car. You can even just cut off the connector and splice the wires individually (this solution costs less but is more permanent). The metal chassis on most head units will also be connected to ground. Figure shows cut and labeled wires that are ready to be spliced.

Figure. Figure. Labeled head unit wires ready for splicing

Adapters for Mounting

Some dashboards have single-height DIN slots for car stereos; other vehicles, such as Chrysler/Dodge/Plymouth cars, use a double-height DIN slot. For a clean install of a single-DIN device in a double-DIN dashboard, you should purchase a universal adapter. This plastic mold fits in the double-DIN slot and accepts a single-DIN device.

If you are installing an aftermarket head unit into a vehicle with a space-age-looking dash, you will have to look online or ask your local installer if they can order an appropriate faceplate adapter. These plastic adapters are made for some popular cars that have strange head unit mountings. If no adapter exists, though, all is not lost: good stereo shops can fabricate a mount using fiberglass, ABS plastic, or other materials, paint it, and install it for a custom but seamless fit. Pretty much anything can be installed into anything if you have the installer custom-fabricate a method of mounting it.

Proprietary Bus Connectors

Recent-model factory head units and higher-end aftermarket head units come equipped with special "buses." Just like USB ports or other standard computer connectors, these vendor-standard buses allow a family of devices to communicate both analog and digital data. CD changers, satellite radios, and other devices connect to the head unit through this bus. In a factory head unit, there might also be some other wires that connect to alarm systems or other parts of the vehicle's electronics.

If you have any of these devices installed, such as a factory CD changer, changing your head unit will most certainly disable it. You generally have to match any add-on equipment to the head unit.

If you are installing a new head unit to make it easier to use external audio sources, take a look at "Get Computer Audio into Your Head Unit" [Hack #14] to ensure that the head unit you want to replace it with has an input adapter for your computer or device. Also make sure that you really have to replace your head unitit's possible that you can get an auxiliary-input adapter to make your (modern) factory head unit do what you want.


Make sure you study up on the car stereo for your car's year, make, and model, either on Google or by studying the shop manuals or asking the dealer. Specifically, you need to know if there are any strange interconnections between your head unit and other necessary car functions. If the head unit goes too far beyond the basic wires listed earlier, stop and get knowledgeable assistance for your specific vehicle.

Some head units are required to be installed for the car alarm to work. If you replace these, you still have to keep the head unit stashed somewhere (for example, under a seat). Some head units integrate closely with features such as OnStar that hook into the car's computer, the airbag system, and so on. In these cases, it may be difficult to find an adapter that preserves the factory safety features, and you may be essentially stuck with your factory head unit. So know before you go, lest you find that the jaws of life never arrive to pry you out of your car because you snipped two wires you didn't recognize, which disabled your OnStar, which prevented it from reporting that your airbag had deployed.

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