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    JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    I知 trying to install an amp and sub to the factory system on a 2004 530i. It has the standard sound system, with a very small subwoofer amp. I知 planning on tapping in to those sub frequencies coming out of the stock subwoofer amp, using a line out converter (speaker level to RCA converter) to a JL 2501 amp which will drive a JL 12w3 sub. I need some opinions on what is what on this stock wiring harness coming out of the small subwoofer amp on the standard U.S. audio system. This is the small silver box on the left side of the trunk. I知 pretty sure I know which ones are the speaker wires, I just don稚 know what the positive and negative wires for each one are, or how to test the polarity. I知 open to suggestions.

    Don't I really just need the sub frequencies the amp is putting out, so as long as I tap into the pair on **one** of the subs, does it matter which way I feed the LOC concerning polarity? Can't I just hook up one of the RCA's to the amp as input?

    Factory wiring harness:
    Going from left to right. SMALL BLACK WIRES-input signal from head unit (MASK computer). FIRST SUBWOOFER PAIR-brown/white stripe, red/blue stripe. SECOND SUBWOOFER PAIR-brown/yellow stripe, red/white stripe. AMP REMOTE TURN-ON-small white wire. POWER-thick red wire. GROUND-thick brown wire.
    Attached Thumbnails Attached Thumbnails JL Sub Amp 2501/JL 12w3 install on factory system questions.....?-amp.jpg  







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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    I would follow the wires to those subs that BMW has to make sure you have the right wires. I would then tap into them wherever you want and use the wire with the brown on it as the negative, I assume it is negative because the system brown is negative. If it is not it will not hurt a thing to go ahead and hook it up and you will not even be able to tell a difference if you have it backwards. Maybe someone will chime in here and tell us how to figure out the polarity on stock wires.




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    It would be great if I could actually remove the subs to look at the wires - That would be my first and obvious choice. However, the stock subs are inaccessible. They are underneath the front seats, and the only way to get at them is to remove the seats. Quite a chore if you ask me. Plus they are covered with a thick metal plate, so I can't even do the old speaker 'pop' test with a D battery because I can't even see the subwoofers underneath the thick metal plates. There has got to be a smarter way to test this - a multimeter, maybe? Would the postive speaker wires show a charge, while the negative ones wouldn't?




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    hello. i am also interested in adding a 250/1 to my factory system in my '05 gmc yukon denali. i will be using a line out converter (speaker level to RCA converter) similar to the one you describe, but i have never tried this before. is it really as simple as splicing into the speaker wires for the factory installed speakers? does it matter where along the speaker wires? what is the prefered method for splicing? thanks.




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    Quote Originally Posted by acribb
    Would the postive speaker wires show a charge, while the negative ones wouldn't?
    no, all i can say is get under that seat some kind of way and do the pop test

    if you cant get under the seat then contact the car dealership you purchased the car from and they should be able to get that information for you




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    Quote Originally Posted by redwings7907
    is it really as simple as splicing into the speaker wires for the factory installed speakers? does it matter where along the speaker wires? what is the prefered method for splicing? thanks.

    yes its thats simple, and no it doesn't matter where you splice into the wire, but i usually connect the convertor directly to the speaker closes to where im going to mount the amp (to keep the factory wiring intact) just make sure you have a really good connection thats not going to come undone



    If your going to connect that amp to a sub make sure it has a low pass filter if it doesn't your going to have to get a crossover.




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    Quote Originally Posted by HAVINGFUN
    use the wire with the brown on it as the negative, I assume it is negative because the system brown is negative. If it is not it will not hurt a thing to go ahead and hook it up and you will not even be able to tell a difference if you have it backwards. Maybe someone will chime in here and tell us how to figure out the polarity on stock wires.


    to test if its negative or not just use an ohm meter connected to a metal surface if it ohms out then its negative if it show's resistance then its not a negative. BUT, how hard would it be to run another ground anyways??




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    Quote Originally Posted by Decipha
    yes its thats simple, and no it doesn't matter where you splice into the wire, but i usually connect the convertor directly to the speaker closes to where im going to mount the amp (to keep the factory wiring intact) just make sure you have a really good connection thats not going to come undone



    If your going to connect that amp to a sub make sure it has a low pass filter if it doesn't your going to have to get a crossover.
    is there a preferred splicing method? what's that about a sub, a low pass filter, and a crossover?




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    Quote Originally Posted by Decipha
    to test if its negative or not just use an ohm meter connected to a metal surface if it ohms out then its negative if it show's resistance then its not a negative. BUT, how hard would it be to run another ground anyways??
    I think we're talking about two different things here. Are you talking about the ground wire for the stock sub amp? Are you saying that a ground is a ground and the ground (-) for the speakers is the same thing as a power ground? I never thought about it like that but, makes sense....I guess the power ground on an amp actually feeds grounding to the polarity on the speakers coming out? Anyways, i'm trying to figure out for sure which is the postive and negative on each speaker. So when I use tap in connectors with speaker wire connected to the factory sub outputs, I can do this test to determine the + and - speaker wires for each sub? In this case, I won't have to pull the seats out then, right?

    As for BMW, I can't even mention the word 'aftermarket' around them. In fact, I am waiting to even install this new sub and amp just because I need to have warranty work done on the car. The factory stereo has a strange intermittent static in all speakers, not just the subs upon initial starting. It's only when starting up the car the second time for the day, usually during a hot day. Static lasts for 10 minutes or so on all sources. I know the first thing BMW would point to would be my aftermarket sub setup, so i'm waiting to put it in until after I take my car in. It's obviously not the factory sub amp, otherwise I would just hear the static from under the seats. I know what the problem is from browsing bimmer boards - and it's a telematics unit causing the static which is also hooked up to the computer/stereo unit.....Sorry for the babble....

    Thanks for any installer help you can give me.
    Last edited by acribb; 03-28-2005 at 09:38 PM.




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    Bumpety bump...




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    Would anyone be able to help out with the above question concerning testing the wires? I'm new at this and just want to get my system set up correctly, with the satisfaction of having done the job myself. Thanks again....




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    Re: JL Sub Amp 2501/JL 12w3 install on factory system questions.....?

    If you are still referring to the +/- to install the line level converter for a sub amp look at my previous post. Use the speaker wire with the brown on it as your negative, it is an AC current and it will not damage anything if you have it backwards. Many people actually reverse the polarity on speakers to get the a better aligned sound system. Try it one way then the other way and whichever sounds better is where you leave it. My Alpine Headunit has a polarity reverse button on it for that reason.




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