Things I Learned from Wiring a Car Stereo

S2000 Wiring Diagram

S2000 Wiring Diagram

So I just finished installing a car stereo into my car. I wanted to do it myself to learn as much a possible. This post is to share bits of information that were previously buried on message boards, or were myths that car audio shops had previously told me (or debunked for me).

DISCLAIMER: I’m not a professional, any of this could be false, I just want to share what I now know.

Running power

  • The entire chassis is grounded. This is why you remove the black contact first when installing a battery; you don’t want the red contact to brush up against the chassis and cause a short.
  • Shorts are bad, because resistance approaches zero, and Voltage=Current*Resistance. Voltage is a constant 12 volts, and all that current gets converted to heat (fire)
  • Install fuses as close to the battery as possible. This reduces the risk of a short by accidentally touching the red wire to the chassis.
  • Your amp should have fuses on it (e.g. mine each had two 25A fuses). Add up the total amperage, and use a fuse near the battery slightly higher than this (I used a 60A fuse going to each amp).
  • Battery power to the amps is DC, while lines going from the amps to the speakers is AC. This is why you need expensive high gauge wire for power, but speaker wire can be relatively thin in comparison.
  • It is a half-myth that electricity travels on the surface of the wire. This is only true for AC power, and should be most current travels on the surface, not all; so high thread-count for AC is important and not for DC. It is called the skin effect, and happens because at every point in a cross section of a wire, magnetic flux is inducing back EMF causing resistance, and the center of the wire is subject to highest amount of this. DC has no alternating flux, so this doesn’t happen, and resistance is even across the cross section of the wire. However high threadcount wire can be bent more before breaking, so it’s easier to snake around corners; that’s really the only advantage of it for power wire.
  • Avoid cheap alloy wires that are copper-coated. You can tell by looking at the ends of the wires where it is cut; it should be solid copper. Pure copper wire is fairly heavy too. If you get this wire, make sure it has low resistance.
  • At high amperages, the resistance of the power wire becomes significant. Calculate amps by watts = amps * volts (where volts is 12). If too much current goes through, too much heat is created which melts the insulation off and the wire touches the chassis which is grounded and causes a short. Since you installed a fuse, it will blow rather than your car catching on fire.
  • When grounding the amps, use the same gauge you used for running power. The same amount of current flows through them. Since the chassis is grounded, they can be terminated by bolting these to the chassis. Sand down the area where they’re bolted, because it’s probably painted (to stop rust and corrosion).

Amps and Speakers

  • Class D amps are good for subwoofers. They are generally 2/1 channel, which means they have 2 channels, but you can “bridge” the two together to get twice the boost for one channel.
  • Ignore the “max” watts of a speaker or amp, and only pay attention to RMS (Root Mean Square), which is essentially the “average” power of a speaker or amp. Don’t buy speakers who don’t list this, unless they are free, which in that case they are probably half of the “rated” power.
  • Pair your amp to your speakers; which means get an amp with slightly more average power than the speakers.
  • It is better to have underpowered speakers than an underpowered amp. If your volume goes too high the amp will start clipping at peaks and troughs. At these points, pure DC is sent over the line rather than AC. DC creates heat which burns out the coils in your speakers. This is how speakers are usually blown.
  • Do not run signal wires parallel to power. If they cross, make it happen perpendicularly. Electrical Induction is a magical thing that you should avoid because it makes phantom buzzing in your music.


  • This is the thing that goes in the dash, and is usually the flashiest and most superficial of things.
  • All Alpine headunits have RCA plugs out that go to the amp. This is not always the case for other makers.
  • There is a blue wire in the wiring harness somewhere; this should be run to the “remote” terminal on your amps. It is how the car tells the stereo that the car is on (rather than parked idle); without this your amps would always be on, and always be draining your battery. It’s very low current, so really thin wire will suffice.


  • They separate high frequencies and low frequencies.
  • These are electrically very simple things. You can build them yourself if you can solder. Don’t spend a lot of money on them.


  • Jkikx8891I tried to install my cars factory wires to the new headunits harness connector thingys wires when i did, it didnt work i done them wrong its my first time trying and now i regret it because when i rewired the wires back to the factory harness th
    Posted December 21, 2014 at 5:53 am | Permalink

    I tried to install my cars factory wires to the new headunits harness connector thingys wires when i did, it didnt work i done them wrong its my first time trying and now i regret it because when i rewired the wires back to the factory harness thingy it dont work neither does my clock/AC etc display, when i used to lock my door it would lock the whole car now it only locks mine the dash fuel temp needles go berzerk as soon as i start the car they jump right up then straight back down sometimes makes you think they going to stick as it sometimes goes back down slow, i never unhooked the battery whilst i was messing around with the wires i have chexked all the fuses in the car but i cant figure it out i put it down to me messing with the wires ive caused something to happen its a mazda 6 2003 model

    • philihp
      Posted January 14, 2015 at 9:45 am | Permalink

      I’m sorry? Good luck.

  • Amy Zheng
    Posted July 20, 2015 at 7:15 am | Permalink

    Hi ,

    Nice to contact you , this is Amy from China .
    We are the factory of custom wire harness assembly for car stereo nearly 10 years .
    Hope we can have a good cooperation .
    Any reply will be appreciated .

    Best regards,
    Amy Zheng
    Huizhou Jingfeng Electronics Co.,ltd
    Lianhe Industrial Park,Shuikou,Huizhou,China (516055)
    TEL : 0752- 2028999(ext.812) FAX : 0752-5801062
    Mobile/Whatsapp: 86-13428059401

  • Posted February 3, 2017 at 2:32 am | Permalink

    You can also have a look at the local area for shops because it is usually
    the best channel in finding the data regarding automobile stereo systems.
    Most enable you to buy online; others suggest you
    to contact them before you purchase second hand to avoid
    compatibility issues. We recommend to hire an trained technician for
    any work on your automobile. You should always inspect their portfolio before you let them work on your automobile.
    It is probably the most significant decisions when choosing the
    retail store to perform work for you. No matter if you purchase
    a brand new stereo system, this is a must. Lots of people claim they can adjust
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    Common question you can ask when inquiring for a stereo system
    is what type of training they have. Every car stereo shop should have a Phase
    Checker to complete the task. If they do not, then search for
    another technician

  • Posted May 6, 2018 at 8:12 am | Permalink

    Amazing Pieces of information

    • Philihp
      Posted August 17, 2018 at 7:01 pm | Permalink

      Glad you liked it!

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