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M2 Technical Topics > Navigation, iDrive, Audio, Video, Bluetooth, Phone, Cameras, Electronics > Rear-Deck Speaker-Wire-Polarity Confirmed

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      02-24-2018, 09:32 AM   #1
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Thumbs up Rear-Deck Speaker-Wire-Polarity Confirmed

As is well known, there is some debate about the polarity of the rear-deck speaker wires on 2-Series cars—see this thread http://www.2addicts.com/forums/showthread.php?t=1258290, beginning with post 17 and the subsequent discussion. Using a multimeter, I have unequivocally determined the polarity of said wires on the driver's side, or left-hand side when looking at the car from behind, on my 2017 BMW M2. I hope this information proves helpful to those of you swapping out the rear-deck speakers.

In short, here is what I found. The wires coming from the BMW amp on the driver's side—or left-hand side when looking at the car from behind—have the following polarity:

brown-striped wire is positive
red-striped wire is negative.

Although the color coding of the wires is reversed from the common convention on the driver's side, a moment's reflection reveals why the polarity is this way. Seeing as (i) the BMW amp-to-speaker plugs are identical on both sides of the rear deck, and (ii) the rear-deck midrange speakers are identical too, one can interchange the speakers from side-to-side without issue. This implies that the wiring from the factory must have the polarity in the same place on the BMW amp-to-speaker plug on both sides, regardless of what the color on the wires implies. This means that members havinfun and ryem3 came to the correct conclusion regrading polarity—nice work guys!

If one uses the BMW pigtails that can be purchased from Ebay, simply plug them in to the BMW amp plug on each side. The red pigtail wire is therefore the positive wire on each side and should be connected to the positive terminal on your speaker. As the first attachment shows, the red wire on the pigtail connects to the brown-striped wire on the BMW amp plug on the driver's side, which as noted above, is positive.

The second two attachments show the multimeter in action. Note that the small spade connector is connected to the red wire on the pigtail, which is then connected to the brown-striped wire from the BMW amp. The positive number for the milliamps confirms this is the positive lead, as the positive lead from the multimeter is connected to it. The negative value on the third attachment indicates the positive lead on the multimeter is connected to the negative lead from the amp.

Cheers!
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      03-06-2019, 06:21 AM   #2
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Thanks! Helpful to know.
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