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

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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: http://www.bimmerfest.com/forums/attachment.php?attachmentid (6651&stc=1&d11702112
Here is another picture from another vehicle: http://www.bimmerfest.com/forums/attachment.php?attachmentid (7281&stc=1&d12154763
And another: http://www.bimmerfest.com/forums/attachment.php?attachmentid &1502&d94537117
And another: http://www.bimmerfest.com/forums/attachment.php?attachmentid )5239&stc=1&d17334573
And another: http://bimmerfest.com/forums/attachment.php?attachmentid07223&d 25771723
And another: http://www.bimmerfest.com/forums/attachment.php?attachmentid 0762&stc=1&d52530849
I could go on (and on); but we can't figure out WHAT the BMW design flaw is. http://bimmerfest.com/forums/showthread.php?t97245
Q: Can you tell from these pictures what the BMW design flaw is?
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On 3/13/2013 8:03 PM, Arthur wrote:

Not unequivocally, of course not, but it would appear likely a temperature/time-hardening of the insulation combined w/ the flexure point eventually fatigues in that general area.
What's the age of the vehicles and condition of insulation in the area? Are the vehicles in very cold or hot climates and not garaged by any chance where such degradation could have been accelerated by extremes?
Is there preferential failure in any given circuit(s)? Perhaps a circuit operating at high capacity relative to wiring ampacity/insulation rating is aiding in the failure mechanism.
What does BMW say?
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dpb wrote on Wed, 13 Mar 2013 20:15:16 -0500:


Yes. All the wires have been identified and all the circuits involved are implicated variously, e.g., KNOWN LOOM WIRE CONNECTIONS: 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[s])/(line color)=(pin number)@(connector number -> description Sizes are 0.35mm2==!AWG, 0.5mm2== AWG, 0.75mm2==AWG

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
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"Arthur"

** Or use silicone coated wire and do it just once.
.... Phil
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Phil Allison wrote on Thu, 14 Mar 2013 16:24:59 +1100:

Here's a picture of the loom, laid out (on a BMW E46 3-series): http://www.bimmerfest.com/forums/attachment.php?attachmentid &5914&d97298236
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this BMW design flaw in all 3,5,7 series BMW trunk wiring looms?:

What do they typically charge for such a replacement? Let me guess: $15,000 That makes sense. Anyone fool enough to by a BMW should be happy to pay for that fix.
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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.
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this BMW design flaw in all 3,5,7 series BMW trunk wiring looms?:

IMO a car with a price like the BMW shouldn't need much repair in the first 10-years. Certainly not like this wiring defect requires.
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Re Re: What is the root of

When you are paying what most BMWs cost, you pay to have it repaired. Most often you do not keep it long enough to need repairing. They are not made to be repaired, but traded every couple of years. It is a status symble, not something ment to last.
While it was only a Mercury at the time, friend of mine had a good thing going. He was friends of a car dealer. A high payed execitive would not let his wife keep a car but 2 years. She seldom drove it. In 2 years the car would have less than 10,000 miles on it. My friend got a great car deal on a slightly used one. Those cars spent most of the time in a garage.
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On Thu, 14 Mar 2013 16:59:40 -0400, "Ralph Mowery"
looms?:

That may be true. If it is, then the resale value will diminish very quickly as the car ages. Is that what happens with these crapolas?
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On 03/13/2013 06:03 PM, Arthur wrote:

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 wire.
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 bend.
#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.
--
fact check required

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On 3/13/2013 6:27 PM, jim beam wrote:

a tiny amount in a product.
Paul
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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.....
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On Thu, 14 Mar 2013 06:18:22 -0700, snipped-for-privacy@optonline.net wrote:

Maybe. But why does it always fail at the same spot.
That can't be due to the poor choice of insulation, can it?
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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 greatest.

No, as you'll notice the conductors are breaking too, not just the wire. So it's a poor choice of insulation AND stranding. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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On 03/14/2013 08:23 AM, Scott Dorsey wrote:

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 failure.
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.
--
fact check required

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

snip
my wife broke the inside passenger side..
i've learned to use only two fingers to pull on the handles, don't grab them.
i agree they are not very rugged... but it's about the only flaw i've found with that car (knock knock)
besides the rear door wires which i understand like the BMW is a very common spot for wires to break on this car...
and interestingly the rear door is used maybe 1/100 of the time compared to the drivers door so you would have to think there is something "special" about the way those particular wires are designed and/or built to make them break before the drivers door wires break
Mark
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On 3/15/2013 5:36 PM, Mark wrote:

The inside handles seem to be designed to break at the 8 to 10 year mark. The have a slot molded in to the highest stress point, I might add I don't see any reason for it. Other than to help the dealer sell replacement handles. Other than the door handles I'm a happy Toyota owner, had a Camry, have a T-100 still a sharp looking truck, have a Lexus and an Avalon. My wife is a persistent patient shopper, and will wait until she finds a great used car at a steal. Mikek
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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 it.
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