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What is the root of this BMW design flaw in all 3,5,7 series BMWtrunk wiring looms?

Discussion in 'Electronic Repair' started by Arthur, Mar 14, 2013.

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  1. Arthur

    Arthur Guest

    Almost every BMW E39 (5-series) and E38 (7-series) and E46 (3-series)
    has shorts that develop in the trunk wiring loom - all in the same spot!

    Here is a picture of the uniformity of the shorts:

    Here is another picture from another vehicle:

    And another:

    And another:

    And another:

    And another:

    I could go on (and on); but we can't figure out WHAT the BMW design flaw is.

    Q: Can you tell from these pictures what the BMW design flaw is?
  2. jim beam

    jim beam Guest

    yeah, it's easy.

    1. the wire coating has a poor grade of plasticizer*, so the coating
    cracks and bending concentrated at the cracked coating will fatigue the

    2. they're using an elbow bend, not a torsion bend. the stress
    concentration at the surface of the wire coating is less with a torsion

    #1 is a factor of the germans being too "green" for their own good and
    not using good old toxic pvc. #2 is the real screw-up - they would know
    that one if they'd spoken to anyone who'd been around the block or had
    done their own testing.

    * the plasticizer used in the wire coating is crucial to give it
    flexibility. the basic polymer insulator extruded over the wire is very
    brittle without it, so a plasticizer is added for flexibility. if the
    plasticizer is too volatile and evaporates over time, the coating will
    become hard and brittle per the original polymer, then crack when
    bending stress exceeds a certain value.
  3. Paul Drahn

    Paul Drahn Guest

    PVC wire insulation contains a lead compound. Ano-no in Europe, even for
    a tiny amount in a product.

  4. jim beam

    jim beam Guest

    i think that was back when they were using lead pigments - hasn't been
    for a while now fwiu. and lead is a no-no here too.

    besides, pvc isn't exactly healthy - i think they now use something
    called "epdm". with the right q.c. and testing, there's no reason that
    insulation should have degraded, and with the right physical layout, no
    reason it should have been challenged even if it did.
  5. Makes me wonder about the door wiring.
  6. Arthur

    Arthur Guest

    dpb wrote on Wed, 13 Mar 2013 20:15:16 -0500:
    All the vehicles are five to ten years old'ish.
    The vehicles are all over the world. Same problem everywhere.
    Yes. All the wires have been identified and all the circuits involved
    are implicated variously, e.g.,
    01. Red/yellow line = 2 @ x712 -> trunk lid light (positive)
    02. Red/black line = 1 @ x1191 Rear lid lock switch (positive)
    03. Gray/yellow line = 3 @ 1377 -> tunk lid locking switch (open signal)
    04. Brown/gray line = 2 @ x709 -> left license plate light (positive)
    05. Gray/Brown line = 4 @ x311 -> zv drive (lid closed)
    06. Gray/black line = 2 @ x710 -> right license plate light (positive)
    07. Gray/Green -> 4 @ x311 -> zv drive rear lid (positive)
    08. White/ Brown line = 3 @ x311 -> ZV to luggage compartment light
    09. Brown = 1 @ x709 -> left license plate light (ground)
    10. Brown = 1 @ x710 -> right license plate light (ground)
    11. Brown = 5 @ x311 -> zv drive ground
    12. Brown = 1 @ x1377 -> trunk lid locking switch (open signal)
    13. Brown/blue line = 2 @ x1191 Rear lid lock switch (unlock)
    NOTE: (majority color)/(line color)=(pin number)@(connector number -> description
    Sizes are 0.35mm2===21AWG, 0.5mm2===20AWG, 0.75mm2===18AWG
    Mostly it's the license plate light, the central locking system, and the trunk
    lid which are affected.
    Same thing BMW always says.
    Replace the entire trunk wiring loom every five years.
    BMW Part number: 61116907260
  7. Phil Allison

    Phil Allison Guest

    ** Or use silicone coated wire and do it just once.

    ..... Phil
  8. Arthur

    Arthur Guest

  9. Nate Nagel

    Nate Nagel Guest

    If you have one of these cars an easy fix is if/when something like that
    fails, to splice in some fine-strand wire which will likely outlive the
    car. A good source for a DIYer is old Fluke leads; don't throw them out
    if you bend a probe!

    As for door wiring, also a common failure on many vehicles... already
    had to repair the speaker wiring where it goes through the door jamb for
    my Jeep Cherokee as has just about every Cherokee owner. So this isn't
    just a BMW problem.

  10. Guest

    And maybe you've found the root cause of the problem.
    Instead of using decent wire suited to the application,
    the Europeans chose to use some green hippie wire,
    that not only costs more, but fails.....
  11. Scott Dorsey

    Scott Dorsey Guest

    My guess is that they are using a wire that isn't designed for high
    flexibility, in an application where high flexibility is important.

    That looks like typical crappy automotive-grade vinyl and normal
    fairly coarse stranded wire.

    It's breaking in the same spot because as the snorkel is moved in and
    out, most of the strees is at that one spot.

    Considering that BMW has been famous for electrical problems since the
    Bavaria was new, this should not surprise you.
  12. Arthur

    Arthur Guest

    VinnyB wrote on Thu, 14 Mar 2013 05:24:43 -0500:
    These 3,4,5 series BMWs are some of the best handling and safest
    vehicles on the planet. The M62, M62TU, M54, M52, & M52TU engines
    are bulletproof, and the suspensions superb.

    Yet, part of owning a bimmer is fixing it yourself. Otherwise you'll
    go broke with the repairs. I know of scores who have "repaired"
    their trunk wiring loom - but I don't know of any who went to the
    stealer to have it replaced.

    I was only answering the question of what BMW says to do.
    We all work on our own vehicles so we repair them ourselves.

    Cost to "repair" is about $20 give or take - but the real question
    is why it breaks in the first place. It looks like, from the discussions,
    a combination of poor choice is insulation plus a badly designed snorkel.
  13. Bimmer Owner

    Bimmer Owner Guest

    Maybe. But why does it always fail at the same spot.

    That can't be due to the poor choice of insulation, can it?
  14. Arthur

    Arthur Guest

    Nate Nagel wrote on Thu, 14 Mar 2013 06:30:59 -0400:
    Luckily the door wiring on these E38, E39, and E46 (7, 5, 3 series) bimmers
    is just fine. It's just something wrong with the way the trunk wiring
    loom is designed that makes it crack in at the same point in all these

    Now, don't even get me started on the BMW window regulators (which
    constantly break on all these bimmers!).
  15. Scott Dorsey

    Scott Dorsey Guest

    Because if you make a loop and you open and close it over and over again,
    it will fail in the center of the loop where the angle of the movement is
    No, as you'll notice the conductors are breaking too, not just the wire.
    So it's a poor choice of insulation AND stranding.
  16. Scott Dorsey

    Scott Dorsey Guest

    That's true, and that might be less expensive than using proper wire. Still,
    there's high-flexibility wire designed for the job, that won't break.
  17. jim beam

    jim beam Guest

    but it's bmw. they won't spend a cent on better engineering that a cent
    on advertising can't brainwash.
  18. jim beam

    jim beam Guest

    respectfully and completely disagree on that. the stranding is
    perfectly fine if the insulation remains intact. once the insulation
    cracks, then you have substantial strain concentrated in just one spot.
    even fine wire high count stranding will break if subject to such a

    the fix is both better wire insulation that doesn't become brittle, AND
    re-routing to avoid the elbow bend. then you can keep using cheap wire
    and don't need to spend money on the expensive hi-flex stuff.
  19. Mark

    Mark Guest

    i had the exact same thing happen in the rear door wiring in a 95
    toyota camry.

  20. Guest

    Of course it can be. If BMW uses some hippie green
    insulation that isn't as pliable as other insulation, then
    the insulation will crack. We can't do a forensic investigation
    from some pics that don't show how it's mounted, how
    much it moves, what tensions are on it, etc. But I'd bet
    that area has more bending, tension, etc than the rest of
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