In general, car audio wiring can be broken down into three main categories:
Power cable, which taps into a car’s electrical system
Signal cable, which carries an un-amplified audio signal from the head unit to the amplifiers
Speaker cable, which sends an amplified signal from the amps to the speakers
Every component in a car audio system needs to draw power from the vehicle’s charging system. Most draw a little, but amplifiers can draw a lot. Typically, the power wire supplied with a head unit or the one added for a signal processor is around 16 gauge, whereas power wire for an amplifier is usually larger.
Gauge relates to the diameter of the wire, as measured by a standard known as American wire gauge (AWG). The higher the gauge, the smaller the wire, and the lower the gauge, the bigger the wire. Gauge sizes run from 40 to 4/0, or four-aught gauge, although wire size usually runs from 10 to 1/0 gauge for most car audio applications. (See Figure 18-1.)
Figure 18-1:
Stinger
1/0-gauge power cable. Courtesy of Stinger
Finding a good gauge
Using the proper gauge wire for an amplifier is crucial. If the power wire between the amplifier and battery is too small, it not only restricts how much power the amp can deliver, but it can create other problems as well. Because the amp operates less efficiently, it creates more heat, and more heat can damage of some of the amplifier’s internal components.
The gauge of the amplifier power wire varies depending on how much current the amplifier demands from a vehicle’s battery, as well as how far the amplifier is located from a vehicle’s battery. Amplifier manufacturers usually recommend in the owner’s manual that you use the minimum-gauge power
wiring necessary for an amplifier. Or you can contact the amplifier manufacturer’s tech support department to ask. Generally, for most amplifiers, proper wire gauge runs from 8 to 4 gauge.
If you are using more than one amplifier, you can figure out the total current draw by adding up the fuse sizes of all of your amplifiers. For example, if you 1^11 have two amplifiers with 30-ampere fuses, you need a power wire capable of carrying at least 60 amperes of current. If in doubt, it’s always a good idea to go a little higher just to be on the safe side.
You’ll also need to determine the distance from the battery to your amplifiers, taking into account any bends or turns along the path of the wire. You don’t need to measure the exact distance down to inches, but you can come up with your best estimate.
The chart in Figure 18-2 from the International Auto Sound Challenge Association (IASCA), which sanctions sound-off competitions, helps you determine the proper power-wire gauge after you know the fuse ratings of your amps and their distance from the battery.
For example, if your amplifiers are drawing 60 amperes of current and the distance to the car’s battery from the amplifiers is 12 feet, you would see where the ampere rating (at the top of the chart) and distance (in the chart’s interior) intersect on the chart. Then trace over to the left side of the chart to see the gauge. In this case, it would be 8 gauge.
Other factors
Beyond proper gauge, other factors you need to consider when selecting power wire for your car audio system are
Strand count: The more strands or individual wires the cable has, the easier it is to bend around corners, and therefore easier to install.
Copper content: If the copper strands that make up the conductor of a cable have a low oxygen content, they supposedly have a lower resistance to the flow of electrical current than regular copper strands. Cables with a high oxygen content can also become brittle with age. Many cable manufacturers tout oxygen-free copper (OFC) as being superior for conducting electricity and longevity.
Jacket material: Car audio amplifier power wiring snakes through a vehicle in areas that are exposed to weather, temperature extremes, and potentially damaging substances such as battery acid. It’s important that the jacket of the power wire, the plastic coating on the outside, be able to stand up to the elements and resist corrosion. As long as you stick with quality cable, the jacket outer coating should be suitable for the automotive environment.
Playing it safe
An important aspect of car audio power wiring is making sure that it’s properly fused. A fuse protects the components in an electrical circuit (in this case, the car audio equipment) and the wiring tying the equipment together. Short for fusible link, a fuse typically contains a small metal wire or strip that melts when a higher amount of electrical current than it can handle flows through it — and, more importantly, when a higher current that the wire and component it’s attached to can handle flows through it. This opens the circuit so that the current flow ceases and doesn’t damage a component or wiring.
Many car audio components come with an onboard fuse to protect their internal circuitry, and some also have a fuse in-line with their power wire, which means that the fuse is inserted into the wire. But an in-line fuse, as well as power wire, isn’t provided with an amplifier (although onboard fuses are sometimes supplied with an amplifier to protect its internal circuitry).
Having an in-line fuse for an amplifier’s power wire is essential. It protects the amplifier, but more importantly, it also safeguards the car and its electrical system. If the vehicle is in an accident that causes the power wire to break, this can cause a short circuit, which means electrical current flows along an unintended path within the vehicle and can possibly start a fire. In this case, the in-line fuse opens the circuit to stop the current from flowing.
In-line fuses are available from your local car audio shop, electronics store, or online. Many all-in-one amplifier wiring kits also come with an in-line fuse.
A circuit breaker can be used in place of a fuse, although this option is uncommon.
The in-line fuse for an amplifier’s power cord should be placed as close to the car’s battery as possible. That way, if a short does occur, the problem doesn’t travel far. If you were to mount an in-line fuse in the trunk next to your amplifiers, for example, the errant electricity would have to travel a long distance — and could potentially do more damage — before the circuit is opened.
Staying grounded
In addition to a power wire, to complete the electrical circuit, every component in a car audio system also needs a ground wire. (The power wire is called the positive and is usually red, and the ground is called the negative and is usually black.) The ground wire provides the return path for the circuit, meaning that it closes the circuit.
In a home’s electrical system, the ground is literally the ground, or the earth the building sits on, and electrical circuits are grounded to the metal plumbing that goes into the earth. In cars, electrical circuits are grounded to the car’s chassis instead of running a cable for every component back to the battery. So much electrical current running along a car’s chassis can create noise problems, which I discuss later on.
With most car audio components, grounding is simply a matter of running a ground cable to a part of the car that’s attached to the chassis, such as the seats. But with amplifiers — which draw more power than any other car audio component and have the potential to cause more damage if something goes wrong or amplify noise if they’re not wired correctly — proper grounding is essential.
Finding a good ground
An amplifier’s ground wire needs to be attached to a solid metal part of the vehicle. If an amp loses its ground, it will find its own ground path, which is not a good thing. The ground path it finds could be via the signal cables that attach the amp to the head unit, which can fry your head unit.
The ground wire must be the same gauge as the power cable, and it should be as short as possible so that it doesn’t add electrical resistance. As resistance increases, the ground becomes less effective and the amplifier works less efficiently. A short ground wire also lessens the chance that it will pick up electrical interference and introduce noise into the system because many other electrical components, both factory and aftermarket, use the car’s chassis as a grounding point. Think of the ground wire as an antenna for electrical interference — the shorter the antenna, the less chance it can pick up interference and hence noise.
Where you mount your amp determines where you ground it. If you mount an amp under the front seat, for example, you can attach the ground to one of the seat’s anchoring bolts. If your amp is mounted in the trunk, the ground can be attached to one of the shock towers (the metal casing around the shock absorbers) or another metal structure.
If there’s no nearby grounding point, you can create your own by drilling a small hole into a metal part of the car, being certain that you first know what’s on the other side. Insert a sheet metal screw with a star washer that the ground wire can in turn be attached to with a ring terminal (see Figure 18-3).
A ring terminal is a small connector that attaches to the cable with a ring that the screw attaches to.
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Figure 18-3:
A Scosche EFX ring terminal.
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You may need to scrape off paint or any other factory coating to get to bare metal for a good ground. If you live in a place where vehicles are prone to rust from salt on the roads or ocean air, you’ll want to treat with rust-proofing or undercoating the area of bare metal that you exposed.
Power accessories
In addition to power and ground cables and an in-line fuse, you may need other power accessories for your car audio system. These include
A power distribution block: If you are using more than one amplifier, instead of running a power wire from the battery to each amp, you can run a single power wire to a power-distribution block (shown in Figure 18-4) and then an individual power wire to each amplifier. A power distribution block can also contain fuses (in case your amps didn’t come with them or for ease of accessibility), in which case it’s known as a fused I power distribution block.
A ground distribution block: This serves the same purpose as a power distribution block, but for the ground wires of an amplifier.
Power terminals and connectors: Never use bare wire to make connections to various parts of a car audio system. Most connections call for specific terminals or connectors. For example, splicing two wires together to extend a wire run calls for a coupler (as shown in Figure 18-5).
Figure 18-4:
A Stinger power distribution block.
Battery terminals: Because a solid connection at the battery is critical for an amplifier, some installers and enthusiasts use battery terminals made especially for car audio purposes. The terminals feature connections for accommodating large-gauge car audio power wire and may have other features, such as a Plexiglas cover and even digital displays that show the battery’s voltage (see Figure 18-6).
Figure 18-5:
A Stinger 4-gauge power- cable coupler.
Courtesy of Stinger
Figure 18-6:
AScosche EFX battery terminal with a digital volt meter.
Courtesy of Scosche
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