Car Audio Wiring
Car Audio Power Wire
Power wire is one of the most important parts of an amplifier installation. The proper gauge is the second most important consideration, next to fusing. The proper gauge should be used so that the amplifier is not choked off by the size limitations of the wire. If you use too small of a power wire you can get a large voltage drop between the battery and the amplifier. This voltage drop can cause distortion in the output and even cause the amplifier to shut off if it is equipped with under-voltage protection. When selecting a power wire, be sure to purchase one that has many hundreds or thousands of strands so that it will be easier to install and will not break when passing around sharp corners. Also make sure that the jacket of the wire is of a material that will resist chemicals such as oil and battery acid that it may encounter in the engine compartment. When running power wire always make sure to cover it in protective wire loom in the engine compartment and to use rubber or plastic grommets when passing through any metal or abrasive surface. Otherwise the power wire can chaff and eventually short out.
To determine the size of the power cable you can also use the IASCA recommended wire size chart.
| System Amperage | 0-4 ft. |
4-7 ft. |
7-10 ft. |
10-13 ft. |
13-16 ft. |
16-19 ft. |
19-22 ft. |
22-28 ft. |
| 0 - 20 | 14 | 12 | 12 | 10 | 10 | 8 | 8 | 8 |
| 20-35 | 12 | 10 | 8 | 8 | 6 | 6 | 6 | 4 |
| 35-50 | 10 | 8 | 8 | 6 | 4 | 4 | 4 | 4 |
| 50-65 | 8 | 8 | 6 | 4 | 4 | 4 | 4 | 2 |
| 68-85 | 6 | 6 | 4 | 4 | 2 | 2 | 2 | 0 |
| 85-105 | 6 | 6 | 4 | 2 | 2 | 2 | 2 | 0 |
| 105-125 | 4 | 4 | 4 | 2 | 0 | 0 | 0 | 0 |
| 125-150 | 2 | 2 | 2 | 0 | 0 | 0 | 0 | 00 |
| IASCA Recommended Wire Size for Various Amperage Draws and Wire Lengths | ||||||||
You can usually figure out the current draw of your system by adding up the fuse sizes of all of your components. For example, if you have two amplifiers that have fuses of 40 amps and 30 amps then you'll need a power wire capable of carrying 70 amps. Determine the distance from your battery to your amplifier mounting location. Make sure you account for any bends and turns in the wire. This is not an exact science but try to get it close. If this distance is 15 feet then you look at the chart and find where the 70 amp row and the 15 foot column intersect. In this example we get 2 gauge wire. The IASCA wire chart tends to run a bit on the generous side. For more help on determining the proper wire gauge please read this article on choosing wire gauge for amplifiers.
A word about fuses. Install an in-line fuse holder (see photo) for the power wire as close as possible to the battery terminal connection (the IASCA and USACi rule is within 18"). VERY, VERY IMPORTANT!!!!! This fuse protects your vehicle from burning up in case the power wiring shorts out. The wire between the fuse and the battery terminal will be unprotected, which is why you want this section to be as short as possible. The fuse size depends on the current the power wire will carry. Consult the owner's manual of your amplifier(s) to find out the maximum current draw of your system. You can also contact the manufacturer and ask them for that information. For multiple amplifiers you will need to add up the maximum current draw of each amplifier. Once you know the maximum current draw you'll know what size fuse to use. For example, if your maximum current draw is 50 amps then you'll need a 50 amp fuse. Do not insert the fuse until all other connections are made.
Car Audio Speaker Wire
Speaker wire is also important in terms of size and strands for the same reasons but the jacket is not as important because it will not see the same chemicals as the power wire. When shopping for speaker wire, look for oxygen free copper (OFC) wiring. The size of your speaker wiring depends on the amount of power going to your speakers and the length of wire from the amplifier to the speakers. Most systems will need to use 16 gauge to 12 gauge wire. Rarely would you want anything larger or smaller than that.
Car Audio Signal Cables
Signal or RCA cables are important for their noise rejection properties. Cables range in price from a couple of dollars to over one hundred dollars a pair. Most cables in the twenty to thirty dollar range (for a twenty foot pair) should be adequate for most listeners and noise situations. Twisted pair cables offer better noise rejection as opposed to coaxial cables (the most common). Twisted pair cables consist of two small gauge wires that are twisted around each other in a helix pattern. Coaxial cables are one small gauge wire jacketed by a braided cable which is then encased in a plastic jacket. The advantage of the twisted pair cables is in the twist. By twisting the cables noise picked up by one cable will be canceled by that same noise in the opposite cable (at least that's the theory). Twisted pair cables can be difficult to find so ask for them specifically when buying RCA cables.
Car Audio Power Capacitors
Power capacitors or Stiffening™ capacitors are used to assist an automobile that has a problem with dimming lights (voltage sag) or to help tighten up the bass. These capacitors store a large amount of power and then release it very quickly when the demand is the greatest from the amplifier. These capacitors release the current much faster than a battery can and do not force the amplifier's power supply to be at a loss (due to a voltage drop) when bass notes and other transients are greatest. Capacitors should be chosen in the ratio of one Farad per thousand watts. Click here to see how a power capacitor is wired in a car audio system.
Car Audio Batteries
If extended engine off listening is desired then a second battery can be useful. Keep in mind that this will put a greater strain on your charging system as well as add several hundred dollars for a second battery, dual battery isolator/relay, and installation charges (or headaches for the DIY'er). If you are having problems with your charging system then you might need a new or larger alternator. Have it checked out by a qualified technician.
Features and terms that may be encountered with regard to wiring are:
Butt Connectors : This type of terminal resembles a long barrel and is used to connect small gauge wires together. These type are crimp terminals and considered less desirable than soldering when soldering is an option. These terminals are also sometimes referred to as crimp connectors though that term can apply to many variations of crimp terminal.
Deep Cycle: A battery usually reserved for marine use that can be drained and replenished many times. While popular years ago many installers have relegated this battery to system use only with a traditional car battery for main power. The Optima Yellow Top is an example of a deep cycle battery.
Farad (F): The base unit of measure for capacitor storage. One farad is very large and is equivalent to one million microfarads (uF).
Gauge: This refers to the diameter of the wire. The smaller the number, the larger the wire. Sixteen is common for speaker wire, eight is common for average size amplifiers, while four gauge and below is used for large amplifiers. For reference, four gauge wire is about the same diameter as the average male pinky finger.
Gel Cell: A type of battery that uses a gel type acid. These batteries can be desirable because they may be mounted upside down without the danger a standard type battery would pose.
Heat Shrink Tubing: A type of insulating plastic that resembles a drinking straw. A small portion of this tube is cut off and placed on a wire before soldering. After the connection is soldered and cooled, the tube is slid over the joint and shrunk around the wires by means of a heat gun or hot hair dryer.
Microfarads (uF): The more common unit used to measure capacitor storage. One million microfarads is equivalent to one Farad.
OFC: An abbreviation for oxygen free copper. This is the most desirable wire to buy and there is really no reason to buy any other kind. As the name implies it is pure copper that is free from oxygen impurities.
Spade Terminals: A type of terminal used on most speakers. The type found on speakers are male spades while the ones used to connect to these terminals are female spades. These terminals are also referred to as quick disconnects though this name can apply to many different types of terminals that come apart quickly.
Voltage Rating: Referring to the amount of voltage a capacitor is rated to handle. The very least a capacitor used for reinforcement should be rated at is 16 volts while 20 volts is much more desirable and available on the slightly more expensive capacitors.
You may also be interested in How to Install Your Own Car Stereo System . It covers many topics including in depth car audio amplifier installation. Click here.
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