I noticed a disconnected wire dangling next to the battery in the trunk of my 2005 BMW 330ci. It was actually a red and blue wire that veered off from the thick red one in the middle of the image. There was a black attachment at the end with 3 prongs inside, you can see the end of it hanging right next to the battery.

I pulled back the carpet wall material to see if it might have gotten pulled out of something and I noticed another wire that was detached. That was a set of 6 black and red wires that fed into an single row, 6-prong connector. You can see it curved upwards and in front of the thick red wire.

What are these used for?

Image: enter image description here

  • 1
    I don't know if this is the case here, but often times it can be from one of two things: a plug used in testing from the factory; a plug which is in the wiring harness which was not used for your model or the option level of your vehicle. Hopefully someone with some Bimmer knowledge can give you a good answer here. Commented Feb 10, 2016 at 0:54

1 Answer 1


I don't remember seeing that harness on my 2001 E46, but all the E90s have them. The general consensus is that it's used in shipping to ensure the battery remains charged. It is perfectly normal to have that harness sitting there unplugged.

  • I don't have those on mine either (a -02). I know some models have cables for cd-changers and/or FM-modules, but IIRC those are on the left side, and uses some 10-pin connector I think
    – Allman
    Commented Feb 10, 2016 at 10:00
  • Correct. The CD changer and the GPS and phone modules all have wiring on the left side of the trunk. As far as I know there are no extra modules which reside on the right side. Further research suggest newer E46s may also have an IBS module, which may be the reason for the battery saving harness. Commented Feb 10, 2016 at 12:11

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