How to Install a Head Unit With No Wiring Harness

Depending on what you mean by "wiring a car radio without a harness," there are a couple of ways to work the problem. If you have the factory harness, but not the harness that came with your head unit when it was new, then you can either buy an adapter—if one is available—or fabricate one yourself.

If you have everything that came with the head unit, but someone, at some point, cut the factory harness out of the car, all you have to do is identify the wires and solder in your head unit. However, when your head unit has no harness and you're dealing with bare wires in your car, that's a more complicated but still doable project.

Wiring a Car Stereo With No Factory Harness

Even though head unit harness adapters allow for plug-and-play head unit installation, it's relatively common for installers to cut the factory harness and solder in the head unit harness during install. If that head unit is removed at a later date, you're left with bare wires, or if you want to upgrade to a new aftermarket head unit, you're forced to cut out the aftermarket harness and start from scratch.

While it may seem daunting to look into your dash and see a wild tangle of wires, this problem is relatively easy to deal with. The best solution is to obtain a wiring diagram for your make and model of car, or go online and search for a diagram or table that shows which wires do what.

If you can find out the colors of the speaker, power, ground, memory keep alive, and any other wires, then all you have to do is locate them in the dash and attach them to the corresponding wires on your head unit.

If you can't find that information online or would rather do things the old-fashioned way, figuring out which wires do what is a straightforward process. With a few basic tools, such as a test light, multimeter, and maybe a 1.5V battery, you can get everything sorted out in a few minutes.

For more information on how to correctly identify the mess of car stereo wires in your dash, check out our basic car stereo wiring primer.

Wiring a Car Stereo With No Head Unit Harness

Wiring a car stereo with no head unit harness is a more complicated challenge that may require some fabrication. Tracking down a new or used harness is the easiest solution. Barring the availability of a new harness, you may be able to find a used one from a local wrecking yard or used parts outlet.

If you can't locate a replacement harness for your car stereo, you have your work cut out for you.

Obtain a pinout diagram for your head unit. The best way to find this is to get the model number of the head unit from the label and then run an internet search. Even if the manufacturer doesn't provide adequate documentation, you may be able to find pinout information on a forum or elsewhere.

If you can't find pinout data for the head unit, that's pretty much a deal-breaker.

Fabricating a New Head Unit Wiring Harness

If you can find the pinout data, then use it to fabricate a new harness. The best way to do this is to obtain a rectangular connector sized to fit your head unit.

In most cases, you need a two-row rectangular header connector with a female socket that is a through-hole mount type. This type of connector is designed to be installed on a circuit board, but it also works in a pinch as the foundation of a replacement car stereo harness.

You may be unable to find a connector with the correct pin spacing and the correct number of pins. While the pin spacing is important, the number of pins isn't. You can either use multiple smaller connectors or cut down a large one to fit, whichever works best.

After you find a pinout diagram and obtain a rectangular connector, you solder wires to each of the pins on the connector and then put heat shrink on each wire to prevent shorts.

If your car still has its factory harness, there are two ways you can complete the installation. Either obtain an adapter that's designed to plug into the harness or fabricate one the same way you did with the one for your head unit.

You can also cut the wires and connect them directly to your new harness, although that shifts new problems onto the next person who tries to upgrade the stereo.

Wiring a Car Stereo With No Harnesses at All

If your head unit doesn't have a harness and someone cut the harness out of your car, you'll have to do a combination of the above methods.

The first step is to obtain a pinout for your head unit and fabricate a new harness. After that, identify all the wires in the dash to determine which ones are for the speakers, power, ground, and so on.

Since there is no factory harness in the picture, you have two options to consider. You can either fashion a new harness for the factory wires that will plug into your head unit harness or solder your head unit harness directly to the factory wires.