Smart & Connected Life Connected Car Tech 221 221 people found this article helpful How to Identify OEM Car Stereo Wires by Jeremy Laukkonen Writer Jeremy Laukkonen is tech writer and the creator of a popular blog and video game startup. He also ghostwrites articles for numerous major trade publications. our editorial process Facebook Twitter LinkedIn Jeremy Laukkonen Updated on March 31, 2020 reviewed by Jessica Kormos Lifewire Tech Review Board Member Jessica Kormos is a writer and editor with 15 years' experience writing articles, copy, and UX content for Tecca.com, Rosenfeld Media, and many others. our review board Article reviewed on May 01, 2020 Jessica Kormos Connected Car Tech Android Auto Apple Carplay Navigation Tweet Share Email Identifying car stereo wires might seem intimidating, but in truth, figuring out the purpose of each wire in a factory car stereo wiring harness is actually pretty easy. You can either track down a wiring diagram for that specific make, model, and year, or you can grab an inexpensive multimeter, which is an essential tool for DIY car stereo wiring projects, and an AA battery, and figure it out on your own. Essentially what you’ll want to do is to locate the battery positive, accessory positive and ground wires, which you can do with a basic tool like a test light or multimeter. You can technically use a test light instead, but it’s a better idea to use a multimeter. Then you’ll just have to check each pair of speaker wires with the 1.5V AA battery, and you're ready to install a new head unit. Maritsa Patrinos / Lifewire Check for Power Whether you&'re dealing with a car stereo, a receiver, or a tuner, most head units have two or three power inputs. One power input is hot all the time, and it’s used for ‘memory keep-alive’ functions like presets and the clock. The other is only hot when the ignition key is on, which prevents the radio from being left on after you've taken the key out. In cases where a vehicle has a third power wire, it is used for a dimmer function that's tied to the headlights and the dash light dimmer switch. The first power you'll want to check for is the constant 12V wire, so set your multimeter to the appropriate scale, connect the ground lead to a known good ground, and touch the other lead to each wire in the speaker wire. When you find one that shows approximately 12V, you have found the constant 12V wire, which is also referred to as the memory wire. Most aftermarket head units will use a yellow wire for this. After you have marked that wire and set it aside, turn the ignition switch on, turn the headlights on, and turn the dimmer switch - if equipped - all the way up. If you find two more wires that show approximately 12V, then turn the dimmer switch down and check again. The wire that shows less than 12V at that point is the dimmer/illumination wire. Most aftermarket head units usually use an orange wire or an orange wire with a white stripe for this. The wire that still shows 12V is the accessory wire, which is usually red in aftermarket wiring harnesses. If only one wire ever had power in this step, it is the accessory wire. Check for Ground With the power wires marked and out of the way, you can move on to checking for the ground wire. In some cases, you’ll get lucky and the ground wire will actually be grounded somewhere that you can actually see, which takes any guesswork out of the equation. Ground wires are also black more often than not, but you shouldn’t just take that for granted. If you can't locate the ground wire visually, then the best way to locate the ground wire is with an ohmmeter. You just have to connect the ohmmeter to a known good ground and then check each of the wires in the car stereo harness for continuity. The one that shows continuity is your ground, and you can move on. You can also check for the ground wire with a test light, although it’s a better idea to use an ohmmeter if you have one. Identifying Speaker Wires Figuring out the speaker wires can be a little more complicated. If the remaining wires are in pairs, where one is a solid color and the other is the same color with a line, then each pair typically goes to the same speaker. You can test this by connecting one wire in the pair to one end of your AA battery and the other end to the other terminal. If you hear a sound come from one of the speakers, then you have identified where those wires go, and you can repeat the process for the other three pairs. In most cases, the solid wire will be positive, but that isn’t always the case. In order to be absolutely certain, you have to actually look at the speaker when you trigger it. If the cone appears to move inward, then you have the polarity reversed. If the wires aren’t in matched sets, then you simply have to choose one, connect it to one terminal of your AA battery, and touch each of the remaining wires to the positive terminal in turn. This is a longer process, but it works just the same.