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Old 02-11-2011, 01:53 AM
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bluebee bluebee is offline
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Location: San Jose, California
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K
This is a lovely trunk loom wiring harness DIY!

Thank you for taking the time to write it up so well for the rest of us to enjoy!

Originally Posted by G. P. Burdell View Post
I wasn't able to locate a complete replacement harness in the BMW parts catalog, so I decided to replace the entire wire bundle that passes from the body to the trunk lid.
One thing that has always surprised me is that I've never found anyone who has purchased the wiring harness for the trunk loom. Yet, very many people have chafed and broken wires (ask me how I know).

As documented in that thread, I even called up local BMW dealerships and asked if anyone orders the appropriate harness; they said no.

I asked the forum if anyone replaced the entire harness (stock OEM), and nobody said they did.

Almost all of us (including me) fix it ourselves ... but (and this is what perplexes me), certainly SOMEONE must be going to the dealer to find the cause of the electrical gremlins that occur when the trunk wiring frays.

Q: What is the DEALER doing (are they replacing the entire harness)?

Originally Posted by G. P. Burdell View Post
18- and 20-gauge wire
Thanks for that hint. I had asked (post #48 over here) what wire size to use and didn't get a decent answer.

Originally Posted by G. P. Burdell View Post
The old harness didn't have a lot of tape wrapping the portion where the wires tend to kink and break.
Methinks the "jury" has determined that the wires are NOT kinking. Yep. Strange as it sounds, at least over in the E39 world, most of us surmise that the wires are being "pulled apart".

Not everyone agrees, but the evidence is showing that the insulation is cracked and pulled apart by a couple of millimeters. Some wires are broken but most are simply missing a length of insulation.

So, if true, the solution "might" be slightly longer wires.

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