Sub/Amp install questions for a '04 530

I haven’t installed an amp since my high school days, and need some advice.  I have an ’04 530 and the battery is in the trunk (luckily).  My application is going to keep the stock stereo which is worked via I-drive – I’m trying to add a sub and amp to the stock system.  I believe I’ve located the stock amp in the trunk and have information from e60.net which outlines which wires are which.  However, my stereo is not the Logic 7 stereo which they have some limited documentation on concerning which wires coming out of the stock amp feed the stock subs under the seats.  How can I check which wires are which to verify the + and – speaker connections for the subs so I can tap into these speaker level inputs to my amp?  I just want to make sure I’m truly catching the bass frequencies, in phase to feed to my amp.  I read something about a 9 volt battery and a pine, p***king the wiring harness, I’m just not exactly sure how to do that.  Does the polarity even matter on a sub setup?  I’m assuming I will only need to tap into one of the stock sub’s wires to feed to the amp, right? 

I’m also going to attempt to build a fiberglass enclosure for the spare tire wheel well.  I’ve done a lot of reading on the subject so far, so ***I THINK*** I can do this.  If I glass it thick enough, will I need any kind of bracing in the middle of the fiberglass enclosure?    I plan on driving a JL Audio 12w3 sub using a JL Audio 2501 amp.

Thanks for any help…….

Let's try that again....

I haven’t installed an amp since my high school days, and need some advice.  I have an ’04 530 and the battery is in the trunk (luckily).  My application is going to keep the stock stereo which is worked via I-drive – I’m trying to add a sub and amp to the stock system.  I believe I’ve located the stock amp in the trunk and have information from e60.net which outlines which wires are which.  However, my stereo is not the Logic 7 stereo which they have some limited documentation on concerning which wires coming out of the stock amp feed the stock subs under the seats.  How can I check which wires are which to verify the + and – speaker connections for the subs so I can tap into these speaker level inputs to my amp?  I just want to make sure I’m truly catching the bass frequencies, in phase to feed to my amp.  I read something about a 9 volt battery and a pine, p***king the wiring harness, I’m just not exactly sure how to do that.  Does the polarity even matter on a sub setup?  I’m assuming I will only need to tap into one of the stock sub’s wires to feed to the amp, right? 

I’m also going to attempt to build a fiberglass enclosure for the spare tire wheel well.  I’ve done a lot of reading on the subject so far, so ***I THINK*** I can do this.  If I glass it thick enough, will I need any kind of bracing in the middle of the fiberglass enclosure?    I plan on driving a JL Audio 12w3 sub using a JL Audio 2501 amp.

Thanks for any help…….

Find the factory sub and the wiring going into it. Make a note of what wire is going to what terminal. Undo the speaker input wires. Take a AA battery that has a + and - terminal and black tape or solder a length of wire, say 6" to each terminal. Touch these wires to the speaker inputs. If the speaker moves outwards then the + terminal on the battery is connected to the + terminal of the speaker. If the speaker moves inwards then you have the + terminal of the speaker connected to the - terminal of the battery, reverse the wires and test again.

If you have dual subs then take a signal from both of them.  A good piece of advice here is to use a better LOC than the one that is built into the amplifier. Buy yourself the Audio Control LC6 + bass remote. This will be a far superior interface to the factory system and with the bass remote, allow you to control the added sub indipendent of the master volume control.

LOC = line output convertor.

www.audiocontrol.com

Thanks for the advice.  However, it is nearly impossible to actually get to the factory sub speakers under the seats unless you actually remove the seat.  The grills over them are a hard thick steel you can't see underneath.  Is there any other way to test the polarity, other than right at the speaker?  Also, why would I need both factory sub speaker level feeds going to the amp?  It's just the low frequencies i'm trying to capture in the amp, right?

Nothing is impossible. You need to either find the wires that go to the sub from the amp (crapshoot) or find the wires going into the sub (ding-ding). Once you find the wires then you can test for polarity. I suggest going to the sub as it will be a known wire rather than a guess. It means removing a seat, so what, I would have to do the same now wouldn't I?

Some amplifiers require a 2 channel input in order to sum a signal to mono, so if you have dual subs, run 2 sets of wires.

Rob, I have a JL Audio 2501 mono amp, and a single JL 12W3v2 (4 ohms) subwoofer.  I only need to tap into one of the subwoofer's pair of wires then feed that to a speaker level to line-level RCA, then the RCA to the input on the amp, right?  The question is, how do I hook up the output of the amp to the speaker?  It's got a ++ -- on it coming out.  Positive to one positive, negative to one negative, right?  Does it really matter if I hook it up in phase, i.e., what if I have the postive of the stock sub going into the negative of the speaker to line converter?  Does it matter?  I'm thining of attaching a 9 volt to a pine, then p***king every wire until I hear some noise out of one of the subwoofers.  Will that work?  If I hear the subwoofer making the noise after I p***k the pine on the right wire, that means I hit the postive of it, right?  I'm a newbie here and REALLY don't want to have to take out the seat.  There's a lot of crap to that damn seat....  Thanks again.

Rob - no offense taken.  I'm on this board because I need help.  If I knew how to do this myself, I wouldn't be here asking questions.  I know this is an "INSTALLER's" board, but maybe you could help out just the same.  I've got the BMW specs on the wire colors to the subwoofers.  I just wanted to know how to double check.  I'll scratch the pine deal, no problem, bad idea.  Maybe you can help me out further. 

I know I am intelligent enough to install an amp and subwoofer.  When you first started installing car stereos, you didn't know what you were doing either, right?  I'm a pretty quick learner and i'm just looking for a little verification here.

Anyhow, if I know the + and - leads of one subwoofer then all I should need to do to capture those sub frequencies is to use some tap-in connectors on those to the converter (in phase), then the pre-amps to the amp.  Then I wire the two postives together on the DVC sub to one postive terminal (output) on my monoblock amp and the 2 negatives together to one negative terminal (output) on the amp, right?  Thanks again for any help.