Installing your own car stereo wiring can be quite simple if the existing wires are in good condition, or fairly complex if they are not. If you need to string your own wires, you should be prepared to remove trim pieces, molding, and carpet. A quality wiring installation job will typically involve stringing the wires inside panels and underneath the carpet so that it is out of sight and can not be damaged. If you feel comfortable with this type of work, the process of installing car stereo wiring is usually more time consuming than complicated.
Before you begin your installation, it is a good idea to determine the sort of stereo system you want. The simplest car stereo system will typically consist of a deck, or head unit, and four speakers. Setups can get progressively more complex from there, including components such as amplifiers, woofers, compact disc (CD) changers, or even video components. You should also determine where each unit will be located in order to find out how much wire will be needed. A lot of the car stereo wiring process will involve simple wires, though components like amps may use home theater-style cables.
In many cases, the existing wires in a vehicle may be reused in a car stereo installation. Many stereo shops have specification catalogs that list the size of the stock speakers, allowing you to purchase replacement parts that will fit. Replacing speakers in this situation often involves disconnecting the old units and attaching the spade terminals to the new ones.
Wiring in a new head unit can also be relatively easy, as both the old stereo and the new unit will often be printed with a graphic to indicate the purpose of each wire. It may also be possible to purchase an adapter that will allow you to plug your new stereo into the factory harness. If there is no adapter available and the old stereo does not have a diagram on it, you may be able to work out the car stereo wiring on your own without much difficulty.
The wires for each speaker are typically paired by color, and the negative wire will have a black tracer. It is often possible to check which wires go to each speaker by briefly touching each pair to a AA battery and listening for static. The power and ground wires can then be checked with a test light. Most vehicles will have one wire that is always hot and another that is energized by the ignition. Once you have worked out the car stereo wiring, you may then match it to the new head unit.
Stringing all new car stereo wiring can be a much more time consuming process. You will typically need to string a power and ground wire to the location of each speaker as well as wires for any other components. To get the best results, you may need to remove paneling or trim pieces, or lift up the carpet to route the wiring. Some applications will allow you to string a single ground wire for the rear speakers, though many stereos require a separate wire for each. You may also need to locate your own power and ground sources for the stereo itself, being careful to tap into circuits you will not overload.