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Thread: FAQ: Connecting your Car PC's Power and Speakers

  1. #1
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    Okay, I'm copying this from my answer to another newbie as it would seem to fit here....

    The stock head unit connector on your car has: 12v line from the battery, 12v acc line, ground, lines out to the speakers (usually 4 pair), and probably other wires for various other functions.

    You cannot draw your power from this connector because the wire is not thick enough for the amount of current you will have to draw, you will end up burning out the wire and possibly starting your car on fire. This is why you must run large cable 4-8 gauge from your battery. You only need to run the positive wire (+)(12v)(red) because the negative (-)(ground)(black) is connected directly to the chassis of the vehicle, so the entire metal frame of the car acts as one big ground wire. This is why you can connect the ground to (almost) any bare metal on your car.

    When installing your carputer, you will need to identify: the acc line, and the 4 PAIRS of wires heading out to your speakers. You will have to either A) Tap these lines, B) Find a corresponding plug or C) Cut the connector off altogether. I suggest C. But you must make sure that you TAPE OFF ANY UNUSED WIRES (with black electrical tape) and LEAVE NO WIRE EXPOSED.

    Now, in order to identify which line is which, you will need either a volt-meter, or multi-meter, or a 12v test light. Since you seem to be technologically uninclined, i suggest the test light. They only cost a dollar, and their operation is simple. You connect one end to a ground and the other end is a probe with a light in it. When you probe a voltage source, the light lights up. You could also connect the wire to a positive line and probe for a ground, but you will not be doing that.
    -----
    Now, with the test light, connect the wire end (usually has an alligator clip) to some bare metal someplace on the body of the car. Turn the ignition on (engine does not have to be running), and begin probing the wires if you find one that lights up the light, then shut the ignition off, if the light goes dark, you have found the acc line. If the light stays on, it is the 12v (positive) line, but you won't be using it anyway. If it is not the acc line, turn the ignition back on and move onto a new wire, and so on, until you identify the acc (accessory) wire.

    NOTE:Red wires are almost always 12v positive wires while black wires are almost always negative ground wires.

    Make sure you identify the 12v positive, the negative ground, and the acc lines and exclude these wires from the next test. Also tape of the 12v positive and ground wires because you will not need them, as you will be running new ones.
    -----
    You will now be finding the speaker wires. Use and AA battery and find any two of the remaining wires and touch one to each end. If you guessed right, you will hear one of your speakers make a scratching sound. Make note that this is a pair and which speaker it goes to, and continue on with the wires that are left until you have identified all of the wires going to your speakers.

    Note: Stock speaker wire pairs are usually different shades of the same color, so try those first if applicable.

    Tape off any wires you have not identified after this process because you will not need them.
    -----
    This is it for identifying which wire is what. But you will need a lot more info in order to complete your install.
    Da_Kooz

  2. #2
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    4-8 gague cable?! what kind of carputer are YOU running? some water-cooled quad-procesor 1000watt system? hahahahaha

  3. #3
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    Yes, makes me wonder. Even a 150W DC-DC supply shouldn't draw more than 15 amps (they're quite efficient for the most part), which should be handled by the stock wiring. (check fuse rating dor radio in fuse box to be sure)
    Sentra CarPuter:
    -InnovaTek 7" LCD touchscreen, Biostar M7VIZ w/ AMD Athlon XP-M @800 MHz 1.1V, 512 RAM, 160G HDD, M-Audio Revolution 5.1, USB Wi-Fi with custom external antenna, Holux GPS and lots of really nice audio bits...

  4. #4
    Jesus Freak antimatter's Avatar
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    What are you smoking... 8 guage is what it needs for any long distance. I wouldn't run 4 gauge but i have 8 gauge running to opus 90w. I was getting alternator whine until i upgraded the wiring
    -Jesus- King of Kings Lord of Lords

  5. #5
    Constant Bitrate emdzey01's Avatar
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    www.bcae1.com. learn it. live it.

    an opus is 150 watts, then it runs about 10-15 feet from your battery. 8 gauge is fine, 10 could also do it, but anything thinner might pose problems. it's true you can't use your stock radio's power wire, but you most definitely won't need 4 gauge wiring. to add to that, 4gauge is thick. really hard to get through your stock firewall, most likely you might have to drill a new hole for it.

    just my .02$
    Brushed Metal for Centrafuse 1.4
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    xenarc 700ts | via epia-m10k | audigy2 nx | holux gm-210 | usb wifi | 40gb 2.5" | slot-load dvd-cdrw | morex 3688 | opus 150w | centrafuse, iguidance

  6. #6
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    Heh, silly people spending too much on wire and not enough on a calculator and an electronics book

  7. #7
    Variable Bitrate
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    It may not be nessesary to run an 4 gauge cable to the rear of the car for just the computer, but it is wise to consider your upgrade path for future use.

    For example, you would not want to run a 10 gauge cable for your computer if you are thinking about adding a Large Subwoofer amplifier later.

    Its better to run a larger gauge cable to a distribution block. This will give you added flexibility to expand your system in the future.
    Is this where the witty comment goes?
    97 Black pearl Mazda Miata MX-5 Carpc V2? maybee..

  8. #8
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    Quote Originally Posted by Stealth97
    It may not be nessesary to run an 4 gauge cable to the rear of the car for just the computer, but it is wise to consider your upgrade path for future use.

    For example, you would not want to run a 10 gauge cable for your computer if you are thinking about adding a Large Subwoofer amplifier later.

    Its better to run a larger gauge cable to a distribution block. This will give you added flexibility to expand your system in the future.

    Most definetly, thatīs what i did infact iīve got 4 gague cables running to a pair of fused distro boxes, but from the distro boxes to my computer iīve got 10 gague cables. The only reason iīve got 4 gague cables is because i calculated all my loads (20A from my crappy pyramid amp for the tops, 30A for the alpine V12 on the subs and 70A on the inverter for whatever accessories) plugged in the length of run and the acceptable voltage drop, and my calculator said 4 gague. That, my friends, is the only proper way to figure out wire gague.

    Again, to break it down, what you need to know before you buy wires:

    1) The length of your cable run (approximate is okay, just overestimate)
    2) The total load on the cable in amps (figure out the most youīll use at one time)
    3) The acceptable voltage drop for your components (STFU! THERE WILL BE A VOLTAGE DROP unless somehow you find superconducting wires. It simply depends on how much drop is acceptable, and considering your carīs voltage will be fluxuating from <7V on a cold start to >14.5V while running, you need to make that decision for yourself, this is the hard part. Usually itīs determined from the minimum supply voltage listed on the spec sheets, but if that minimum voltage is below your carīs minimum starting output then either the spec sheet is lying, or you need a new battery with lower internal resistance)

    Values 2 and 3 will give you a number of acceptable ohms for the cable, and cable resistance is based on cross-sectional area, length and conductor material. Youīll probably be using copper, you know the approximate length and the acceptable resistance, from that you can determine the cross-sectional area and therefore the wire gague.

    google the equations yourself! good luck folks

  9. #9
    FLAC aoLhaTer's Avatar
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    For personal refeence, I use 12 guage cable as recommended by Opus and have no problems. Ive used 12 gauge with both an Opus 90 and a 150

    Also, instead of expensive RCA interconnects I use RG6 coaxial cable with RCA adapters on both ends. Its significantly less expensive and will provide the same quality and better shielding.

  10. #10
    Lum
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    Variable Bitrate Lum's Avatar
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    On this subject, those of us in Europe have it a bit easier as the car will either provide an ISO connector or you can buy an ISO adaptor from a store (Halfords in the UK sell them) at which point your wiring will have standard colours and positions.
    Beware of VW / Audi cars and a couple of others which as standard swap the power and ACC lines. Either swap them back or buy an ISO adaptor. The colours are then as follows:

    Power Section:
    +12v (battery) - Yellow
    +12v (acc) - Red
    Earth - Black or Brown
    Power Aerial / Amplifier switch on[1] - Blue
    Phone Mute[2] - Purple
    Immumination[3] - Orange
    There are two unused pins. Some cars will use these for their own purposes. Best left alone

    Speaker Section (note that each speaker has a coloured wire for + and a colour+black for -)
    Rear Right - Purple
    Front Right - Grey
    Front Left - White
    Rear Left - Green

    For diagrams see: http://www.incarsound.co.uk/wiring_diagrams.htm

    [1] Note: many head units provide a separate connector to use for signalling external amps to switch on and advise not to use the power aerial line for anything except the aerial

    [2] If this wire is earthed the radio (or Car PC) should go into mute. A separate car handsfree kit will then switch this as and when calls arrive. No point connecting it if your Car PC is doing bluetooth handsfree

    [3] IIRC this one gets power when your dashboard lights come on, typically this would happen as soon as you switch the sidelights come on. You may be able to do something with this to trigger a brightness change on your LCD or something.

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