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Thread: Bad to use power/gnd wires on OEM harness?

  1. #1
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    Angry Bad to use power/gnd wires on OEM harness?

    I recently purchased a harness adapter for my Hyundai Accent. The aftermarket harness adapter uses the same wire thickness (~16ga I think) as the stock radio plug. The speaker and power wires go into the bowels of the car as one big bundle.

    Is it bad that the signal and power wires are together? Using better wire or routing power wires far away is pointless if they will eventually be in one bundle anyway. Plus, I can't rewire that whole area easily.

    My specific question is:

    Is it OK if I use the stock radio harness, but ground it close to the amp? Right now I am using both the 12v and ground wires from the harness, so the ground wire is pretty long. I have alternator whine. Will grounding the amp with a very short wire fix the whine? Will I have to install a separate 12v wire and ignore the 12v wire on the harness?

  2. #2
    Fusion Brain Creator 2k1Toaster's Avatar
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    The 12v constant wire on the harness just isn't built to allow that much current to pass through it. It is meant for a radio, not a computer. Always is reccommended to run a thick wire directly from battery to the PSU. Then an equally thick wire for your ground. The 12v switched can still come from the radio harness, becuase it is just a signal type wire. Doesn't actually draw anything worthwhile...

    And yes a shorter ground will help with the whine, but it is still like trying to suck a drink out of a coffee stirrer. It will work, but eventually you die... Well something like that.
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    Quote Originally Posted by 2k1Toaster
    The 12v constant wire on the harness just isn't built to allow that much current to pass through it. It is meant for a radio, not a computer. Always is reccommended to run a thick wire directly from battery to the PSU. Then an equally thick wire for your ground. The 12v switched can still come from the radio harness, becuase it is just a signal type wire. Doesn't actually draw anything worthwhile...

    And yes a shorter ground will help with the whine, but it is still like trying to suck a drink out of a coffee stirrer. It will work, but eventually you die... Well something like that.
    I am powering a small-ish amp, not a car computer. The stock headunit was a radio/tape player that could drive the speakers at a reasonably nice level. I'm sure I can pull decent current through it. The question is alternator whine: will the short ground wire fix it (still using the 12v on the harness), or will I have to install dedicated power wires?

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    Fusion Brain Creator 2k1Toaster's Avatar
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    Quote Originally Posted by aec merlin
    What do you mean that the 12v is a signal wire?
    I mean that it passes 12 volts through it, but at very low amperage, hence a skinny wire is acceptable. It just "signals" the PC or amp when to turn on, and then it sucks it juice through the dedicated 12v constant.

    And to answer your question more bluntly:

    A short ground is always a good thing. Less chance to pick up interferance. Just make sure the wire is thick enough and ground to a good spot.
    As to running a new wire, I would. And make sure it is fused too.
    Watts = Volts x Amps
    Obviously in most car environments, it is 12 volts. Lets say you run a 200 watt RMS amp (Not too familiar with amps btw, just physics). That is 200/12 amps or 16 amps. Now, music rarely ever pushes the limit so on average it will be about a third of this (5 amps), but there are times when it needs to draw 16, and it will try to. Now, according to the awg specificiations table, the maximum current a 10 guage wire can draw safely is 15amps. Too little, so eventually, kablewy. So go up one or two to 9 or 8 awg.

    16awg can carry a maximum of 3.7amps safely. If you are running more than this, then eventually you will have problems. Refer to **here** for numbers.

    So basically, your headunit will run fine. Plug in your amp and yes it will work, but less and less over time and as the wire heats up, melts, sparks on the chassis, and lights you on fire while driving down the interstate.

    To sum up:
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  5. #5
    Fusion Brain Creator 2k1Toaster's Avatar
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    High tech btw...
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  6. #6
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    Quote Originally Posted by 2k1Toaster
    I mean that it passes 12 volts through it, but at very low amperage, hence a skinny wire is acceptable. It just "signals" the PC or amp when to turn on, and then it sucks it juice through the dedicated 12v constant.
    Haha, yes, I understand what a signal wire is. Sorry if I worded my question incorrectly -- I assumed you would realize that I was talking about the constant 12v on the harness and not the amp-turn-on wire. Either way, the wires on the harness are all the same thickness.

    My question still stands, though:

    I have read that power wires should not be placed near signal (speaker) wires as this will cause interference. Sure, I can route signal wires on one side of the car and power wires on the other, but they all end up next to each other anyway when they reach the harness. Is this one of the causes of my alternator whine (besides bad ground)? Is it pointless to separate them since they go into one big bundle anyway (inside the dash)? Is the proximity of the speaker wires to the power wires going to affect sound quality at all?


    PS: The amp I am using is this piece of junk. It is driving stock speakers. I got it for free so I am not complaining.

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