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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #26  
Old 01-24-2011, 01:01 PM
G. P. Burdell's Avatar
G. P. Burdell G. P. Burdell is offline
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Location: Southeastern U.S.
 
Join Date: Jan 2006
Posts: 1,734
Mein Auto: E46
Quote:
Originally Posted by bluebee View Post
I'd suggest you guys perform a similar ad-hoc wire-identification task force.
All it takes is one person with a Bentley manual and a bit of free time. I've taken copious notes from the electrical diagrams and have tentatively identified all of the wires in the bundle. Prior to re-wiring the trunk lid, I will confirm their functions and markings. (I already know that at least two wires have markings that differ from the diagrams.)

After I've completed the repair, I'll post my findings.
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  #27  
Old 01-24-2011, 04:43 PM
Variocam Variocam is offline
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Thanks very much. Although I suppose all it would take is to get access to the reverse light (anybody know if this should be done from the outside by removing the lenses, or from inside the trunk by removing the paneling on the inside of the trunk lid?), and matching up the wiring there with what's in the bundle, right...?
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  #28  
Old 01-24-2011, 10:29 PM
bluebee's Avatar
bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K
Quote:
Originally Posted by Variocam View Post
all it would take is to get access to the reverse light
That would solve ONE problem but not the BIG PICTURE.

G. P. Burdell and I were talking about adding value to the big picture by identifying ALL the wires on the E46 (just as we did on the E39).

Once that happens, it's much easier to determine which problems can be related to the trunk loom - and - which will have no bearing on the trunk loom.

It almost never makes sense to solve the little picture ... that's the whole point of the forums ... to increase knowledge and add value in every post!

Good luck!
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  #29  
Old 01-25-2011, 04:58 AM
G. P. Burdell's Avatar
G. P. Burdell G. P. Burdell is offline
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Location: Southeastern U.S.
 
Join Date: Jan 2006
Posts: 1,734
Mein Auto: E46
Quote:
Originally Posted by Variocam View Post
Thanks very much. Although I suppose all it would take is to get access to the reverse light (anybody know if this should be done from the outside by removing the lenses, or from inside the trunk by removing the paneling on the inside of the trunk lid?), and matching up the wiring there with what's in the bundle, right...?
The trunk tail light lenses can't be removed from the outside. Remove the trunk tool kit and gray liner to expose all of the electrical devices and their connectors. With the help of a multimeter or test light - and making sure to keep the car stationary! - identify the wires for the reverse lights, and then trace them back into the right side of the trunk. As I may have mentioned to you in another thread, you'll probably find that they end up at the output terminal(s) of the reverse light relay.
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  #30  
Old 01-25-2011, 04:04 PM
Variocam Variocam is offline
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Location: Austin, TX
 
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Thanks, that helps a lot.
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  #31  
Old 02-09-2011, 04:53 PM
G. P. Burdell's Avatar
G. P. Burdell G. P. Burdell is offline
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Location: Southeastern U.S.
 
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Mein Auto: E46
Update:

I finally found the time to rebuild my car's trunk wire harness. I say that I rebuilt the harness because, once I was done, there wasn't much left of the old harness. Here's my writeup for anyone wanting to do the same.

Introduction

This work took me an entire day from start to finish. I will readily admit that I'm not the fastest DIYer; I frequently stop and take the time to document the process with written notes and plenty of photographs for future reference. On this task, I checked and re-checked my work several times to make sure I spliced the right wires to each other. These checks involved numbering the wires and testing for continuity, both in the car and on the bench.

The temporary repair I made about a month ago held just fine, but I had to make an inline splice right in the area of the harness where the original ground wire had broken. The splice would eventually have broken, or it would have chafed against the other wires in the harness (one of which was looking rather kinked already) and caused more damage. Furthermore, in order to find the broken wire, I had cut into the existing corrugated EPDM rubber cover that protects the harness and seals out water. 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.


Disclaimer

I AM NOT A BMW TECHNICIAN. I am sharing my experience based on the repair I made to my E46 sedan. Depending on the year and configuration of your vehicle, your car's wiring may vary. I will not be responsible for any damage or injury that results from following anything I have posted in this thread. Verify part numbers before you purchase your own materials. It is your responsibility to also verify technical information with a trusted source, such as BMW TIS, your copy of the Bentley Publishers repair manual, or a reputable mechanic. If you are not comfortable with doing this work on your own car, I recommend that you seek the assistance of an experienced friend or your mechanic. Use appropriate safety measures and have proper ventilation when working with heat shrink materials inside the trunk. As always, you are welcome to do things differently and discuss your method here.


Materials

Most of these products, except for the ones with BMW part numbers, are available from vendors such as McMaster-Carr.
  • Wire. I used irradiated PVC (XLPVC) insulated wire in 18- and 20-gauge sizes.
  • 18-to-22-gauge splices. I chose butt splices that are insulated with adhesive-lined heat shrink for the best moisture resistance. Others may choose to solder and heat shrink.
  • Zip ties
  • Wire markers. I have a book of self-adhesive, preprinted Tyvek wire markers that I used to number the wires sequentially, from 1 to 16.
  • Electrical tape. Not for wrapping the entire harness, but used in small quantities for bundling wires together at certain points.
  • Fabric tape. A 15-meter (45-foot) roll is BMW P/N 61 13 6 908 716. Dealer list is $17.72. The factory harness, along with most other interior wire harnesses in the car, is wrapped in a fabric tape that's similar to this tape.
  • Rubber covering. The replacement for the cover for a sedan is BMW P/N 61 13 8 366 627. Dealer list price as of the date of this posting is $6.38.
  • Painter's tape

Tools
  • Common sense
  • Patience
  • Bentley manual
  • Safety glasses
  • Headlamp
  • Disposable gloves
  • Wire cutter & stripper tool
  • Crimping tools
  • String
  • Ratchet and 10mm socket
  • Plastic pry tool
  • Phillips head screwdriver
  • Multimeter
  • Heat gun

The Process

The basic steps involved were:
  1. Disconnect battery. Disassemble trunk lid and right side of trunk.
  2. Identify and number wires and connectors.
  3. Pull old harness out of trunk lid and into trunk.
  4. Test for continuity to confirm wire assignments.
  5. Cut old wire harness out of car.
  6. Build new harness on the bench from pigtails of existing connectors.
  7. Test continuity of new harness on the bench.
  8. Reinstall new harness into trunk and trunk lid.
  9. Splice new harness into existing wires in trunk.
  10. Reconnect battery and test trunk lights, license plate lights, and central locking functions.
  11. Put trunk back together.

Observations
  • This is not a job to rush through. I had to get to work the next morning, and splicing the wrong wires together could have shorted out a component, blown fuses, and resulted in a lot of cussing.
  • Before starting the work, I wrote down and numbered the wires, then researched the Bentley manual electrical diagrams to make sure that I knew the size of each wire and the appropriate size of the wire I would splice in. The wire sizes in the BMW literature (and hence the Bentley manual) are in metric units, so I did a Google search to find a table that lists metric and equivalent SAE and AWG wire sizes. SAE and AWG wire sizes are not the same; AWG wire sizes are slightly larger than SAE.
  • I bought a few different colors of 18- and 20-gauge wire and planned the colors I would use for each splice. For example, I replaced all of the brown ground wires with black wire. It's not completely necessary, but it helped me to identify the wires in the rebuilt harness a little more easily.
  • The existing wire harness is wrapped in a fabric tape whose adhesive has broken down with age and exposure to heat. Just touching the tape left my hands feeling sticky. For the more involved work with the old harness, I wore disposable gloves to keep the goop off of my hands.
  • Before pulling the old harness from the trunk lid, I tied a piece of string to the last connector on the harness. I pulled the old harness out of the trunk lid and untied the string only after it had entered the trunk. This piece of string was my pull cord that would help me to feed the rebuilt harness into the trunk lid.
  • Very Important Thing No. 1: Before cutting the old harness out of the car, I checked each wire for continuity. I picked a portion of the old harness that wouldn't remain in the car and stripped the insulation off of each wire, one by one, to check continuity and number the wires in the trunk. The good news is that the majority of the wires are unique in terms of their insulation and stripe colors, and the grounds that don't go back to the LCM or the General Module all go to a single ground point (X498) inside the trunk.
  • I rebuilt the harness on the bench. I put strips of painter's tape down on the bench and traced the old harness onto the tape with a marker. I marked where each branch came off of the main harness and noted which connector/device was on that branch. Next, I marked the locations of the splices I would make for each branch. I cut the old connectors, each with lots of the original wire still attached, off of the harness and discarded the old harness. I cleaned the old adhesive off of the pigtails and spliced the new wires to these pigtails, one by one, according to the "map" I had drawn on the tape on the bench.
  • After checking continuity for a second time, I wrapped the completed harness in fabric tape. In addition to protecting the harness from chafing against the sharp edges of the trunk lid as I reinstalled it, wrapping the new harness in this tape helps to prevent it from rattling around in there. The old harness didn't have a lot of tape wrapping the portion where the wires tend to kink and break. I wrapped this area completely in an effort to give the wires more support.
  • Very Important Thing No. 2: The hole where the wires enter the trunk lid isn't very large. Splicing all 16 wires at one point along the harness and then feeding it back into the trunk would not have worked, because the resulting bundle would not have been able to fit through that hole. I staggered the splices so that only three or four passed through the hole at a given time.
  • I left plenty of excess wire on the trunk side of the rebuilt harness so that I would have lots of slack inside the trunk. More slack meant that I could make splices more easily without bringing the heat gun too close to paint, carpet, or plastic inside the trunk. I wound up with about a foot of slack inside the trunk.
  • 16 wires x 2 splices per wire x 2 crimps per splice = 64 crimps. A ratcheting crimp tool saved me from some serious hand fatigue.
  • Very Important Thing No. 3: Before making splices in the trunk, I made sure to put the new rubber cover on the rebuilt harness! It would have been very bad if I had forgotten to put it on there before making all of those splices.
  • The inside of the trunk lid is full of sharp surfaces. I didn't wear gloves while feeding the rebuilt harness into the trunk lid, and my fingers had more than a few tiny cuts by the time I was finished. Disposable gloves might help prevent this from happening.
  • I had a fire extinguisher close at hand when applying heat to the splices in the trunk, just in case. The Tyvek wire markers will not survive exposure to a heat gun. When using a heat gun, it helps to have the nozzle attachment that's made for use with heat shrink.
  • After finishing all of the splices and testing the trunk lid devices, I tied back the bundle with zip ties to prevent strain on the splices.

Whew! That was a lot of work, but now I have all new wires passing from the body to the trunk lid. We'll see how long the new bundle and its tougher-than-regular-PVC insulation lasts. BMW could make this repair a lot easier and more convenient if they would produce and sell an affordable replacement harness like they did for the E36.
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Last edited by G. P. Burdell; 02-09-2011 at 05:11 PM.
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  #32  
Old 02-09-2011, 07:08 PM
catso's Avatar
catso catso is offline
catso
Location: Chicago
 
Join Date: Dec 2009
Posts: 2,902
Mein Auto: 2000 323i, 1988 528e
Quote:
Originally Posted by G. P. Burdell View Post
Update:

I finally found the time to rebuild my car's trunk wire harness. I say that I rebuilt the harness because, once I was done, there wasn't much left of the old harness. Here's my writeup for anyone wanting to do the same.

Introduction

This work took me an entire day from start to finish. I will readily admit that I'm not the fastest DIYer; I frequently stop and take the time to document the process with written notes and plenty of photographs for future reference. On this task, I checked and re-checked my work several times to make sure I spliced the right wires to each other. These checks involved numbering the wires and testing for continuity, both in the car and on the bench.

The temporary repair I made about a month ago held just fine, but I had to make an inline splice right in the area of the harness where the original ground wire had broken. The splice would eventually have broken, or it would have chafed against the other wires in the harness (one of which was looking rather kinked already) and caused more damage. Furthermore, in order to find the broken wire, I had cut into the existing corrugated EPDM rubber cover that protects the harness and seals out water. 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.


Disclaimer

I AM NOT A BMW TECHNICIAN. I am sharing my experience based on the repair I made to my E46 sedan. Depending on the year and configuration of your vehicle, your car's wiring may vary. I will not be responsible for any damage or injury that results from following anything I have posted in this thread. Verify part numbers before you purchase your own materials. It is your responsibility to also verify technical information with a trusted source, such as BMW TIS, your copy of the Bentley Publishers repair manual, or a reputable mechanic. If you are not comfortable with doing this work on your own car, I recommend that you seek the assistance of an experienced friend or your mechanic. Use appropriate safety measures and have proper ventilation when working with heat shrink materials inside the trunk. As always, you are welcome to do things differently and discuss your method here.


Materials

Most of these products, except for the ones with BMW part numbers, are available from vendors such as McMaster-Carr.
  • Wire. I used irradiated PVC (XLPVC) insulated wire in 18- and 20-gauge sizes.
  • 18-to-22-gauge splices. I chose butt splices that are insulated with adhesive-lined heat shrink for the best moisture resistance. Others may choose to solder and heat shrink.
  • Zip ties
  • Wire markers. I have a book of self-adhesive, preprinted Tyvek wire markers that I used to number the wires sequentially, from 1 to 16.
  • Electrical tape. Not for wrapping the entire harness, but used in small quantities for bundling wires together at certain points.
  • Fabric tape. A 15-meter (45-foot) roll is BMW P/N 61 13 6 908 716. Dealer list is $17.72. The factory harness, along with most other interior wire harnesses in the car, is wrapped in a fabric tape that's similar to this tape.
  • Rubber covering. The replacement for the cover for a sedan is BMW P/N 61 13 8 366 627. Dealer list price as of the date of this posting is $6.38.
  • Painter's tape

Tools
  • Common sense
  • Patience
  • Bentley manual
  • Safety glasses
  • Headlamp
  • Disposable gloves
  • Wire cutter & stripper tool
  • Crimping tools
  • String
  • Ratchet and 10mm socket
  • Plastic pry tool
  • Phillips head screwdriver
  • Multimeter
  • Heat gun

The Process

The basic steps involved were:
  1. Disconnect battery. Disassemble trunk lid and right side of trunk.
  2. Identify and number wires and connectors.
  3. Pull old harness out of trunk lid and into trunk.
  4. Test for continuity to confirm wire assignments.
  5. Cut old wire harness out of car.
  6. Build new harness on the bench from pigtails of existing connectors.
  7. Test continuity of new harness on the bench.
  8. Reinstall new harness into trunk and trunk lid.
  9. Splice new harness into existing wires in trunk.
  10. Reconnect battery and test trunk lights, license plate lights, and central locking functions.
  11. Put trunk back together.

Observations
  • This is not a job to rush through. I had to get to work the next morning, and splicing the wrong wires together could have shorted out a component, blown fuses, and resulted in a lot of cussing.
  • Before starting the work, I wrote down and numbered the wires, then researched the Bentley manual electrical diagrams to make sure that I knew the size of each wire and the appropriate size of the wire I would splice in. The wire sizes in the BMW literature (and hence the Bentley manual) are in metric units, so I did a Google search to find a table that lists metric and equivalent SAE and AWG wire sizes. SAE and AWG wire sizes are not the same; AWG wire sizes are slightly larger than SAE.
  • I bought a few different colors of 18- and 20-gauge wire and planned the colors I would use for each splice. For example, I replaced all of the brown ground wires with black wire. It's not completely necessary, but it helped me to identify the wires in the rebuilt harness a little more easily.
  • The existing wire harness is wrapped in a fabric tape whose adhesive has broken down with age and exposure to heat. Just touching the tape left my hands feeling sticky. For the more involved work with the old harness, I wore disposable gloves to keep the goop off of my hands.
  • Before pulling the old harness from the trunk lid, I tied a piece of string to the last connector on the harness. I pulled the old harness out of the trunk lid and untied the string only after it had entered the trunk. This piece of string was my pull cord that would help me to feed the rebuilt harness into the trunk lid.
  • Very Important Thing No. 1: Before cutting the old harness out of the car, I checked each wire for continuity. I picked a portion of the old harness that wouldn't remain in the car and stripped the insulation off of each wire, one by one, to check continuity and number the wires in the trunk. The good news is that the majority of the wires are unique in terms of their insulation and stripe colors, and the grounds that don't go back to the LCM or the General Module all go to a single ground point (X498) inside the trunk.
  • I rebuilt the harness on the bench. I put strips of painter's tape down on the bench and traced the old harness onto the tape with a marker. I marked where each branch came off of the main harness and noted which connector/device was on that branch. Next, I marked the locations of the splices I would make for each branch. I cut the old connectors, each with lots of the original wire still attached, off of the harness and discarded the old harness. I cleaned the old adhesive off of the pigtails and spliced the new wires to these pigtails, one by one, according to the "map" I had drawn on the tape on the bench.
  • After checking continuity for a second time, I wrapped the completed harness in fabric tape. In addition to protecting the harness from chafing against the sharp edges of the trunk lid as I reinstalled it, wrapping the new harness in this tape helps to prevent it from rattling around in there. The old harness didn't have a lot of tape wrapping the portion where the wires tend to kink and break. I wrapped this area completely in an effort to give the wires more support.
  • Very Important Thing No. 2: The hole where the wires enter the trunk lid isn't very large. Splicing all 16 wires at one point along the harness and then feeding it back into the trunk would not have worked, because the resulting bundle would not have been able to fit through that hole. I staggered the splices so that only three or four passed through the hole at a given time.
  • I left plenty of excess wire on the trunk side of the rebuilt harness so that I would have lots of slack inside the trunk. More slack meant that I could make splices more easily without bringing the heat gun too close to paint, carpet, or plastic inside the trunk. I wound up with about a foot of slack inside the trunk.
  • 16 wires x 2 splices per wire x 2 crimps per splice = 64 crimps. A ratcheting crimp tool saved me from some serious hand fatigue.
  • Very Important Thing No. 3: Before making splices in the trunk, I made sure to put the new rubber cover on the rebuilt harness! It would have been very bad if I had forgotten to put it on there before making all of those splices.
  • The inside of the trunk lid is full of sharp surfaces. I didn't wear gloves while feeding the rebuilt harness into the trunk lid, and my fingers had more than a few tiny cuts by the time I was finished. Disposable gloves might help prevent this from happening.
  • I had a fire extinguisher close at hand when applying heat to the splices in the trunk, just in case. The Tyvek wire markers will not survive exposure to a heat gun. When using a heat gun, it helps to have the nozzle attachment that's made for use with heat shrink.
  • After finishing all of the splices and testing the trunk lid devices, I tied back the bundle with zip ties to prevent strain on the splices.

Whew! That was a lot of work, but now I have all new wires passing from the body to the trunk lid. We'll see how long the new bundle and its tougher-than-regular-PVC insulation lasts. BMW could make this repair a lot easier and more convenient if they would produce and sell an affordable replacement harness like they did for the E36.
Great work.
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  #33  
Old 02-11-2011, 01:53 AM
bluebee's Avatar
bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 20,076
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!

Quote:
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)?

Quote:
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.

Quote:
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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  #34  
Old 02-11-2011, 02:23 PM
G. P. Burdell's Avatar
G. P. Burdell G. P. Burdell is offline
Rambling Wreck
Location: Southeastern U.S.
 
Join Date: Jan 2006
Posts: 1,734
Mein Auto: E46
Quote:
Originally Posted by catso View Post
Great work.
Thank you!

Quote:
Originally Posted by bluebee View Post
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!
Thank you too, and you're welcome.

Quote:
Originally Posted by bluebee View Post
One thing that has always surprised me is that I've never found anyone who has purchased the wiring harness for the trunk loom.
E36ers can get their hands on a replacement harness that doesn't cost the moon. This is the harness I purchased when I had an E36:

http://www.realoem.com/bmw/showparts...05&hg=61&fg=10

RealOEM shows a ~$160 harness (No. 4 in the diagram below) for the E39 - is it a complete replacement harness, or would that be the $1,300 one?

http://www.realoem.com/bmw/showparts...35&hg=61&fg=10

So far, I don't know that there is a dedicated repair kit for the E46. I guess it depends on whether BMW NA and the service departments across the country have determined that this is a necessary repair kit. Hopefully, BMW NA will begin to stock them for the E46 as the last coupes start to show signs of wiring damage.

Quote:
Originally Posted by bluebee View Post
I asked the forum if anyone replaced the entire harness (stock OEM), and nobody said they did.
They may not realize that it exists, or that it's a far better alternative to patching up the existing wiring.

Quote:
Originally Posted by bluebee View Post
Thanks for that hint. I had asked (post #48 over here) what wire size to use and didn't get a decent answer.
You should be able to find the wire sizes in the Bentley electrical diagrams. Even if the wire sizes aren't listed, it's easy to figure them out in situ.

Quote:
Originally Posted by bluebee View Post
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.
I think we'll have to agree to disagree here. The PVC insulation and the individual copper strands in the wires can only take so much flexing before they fail. A "shortening" of 2mm could indicate shrinkage of the PVC. Does an unrepaired, standard-length harness feel as if it is under tension when the trunk lid is all the way open?

Last edited by G. P. Burdell; 02-11-2011 at 03:30 PM.
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  #35  
Old 02-12-2011, 12:03 AM
bluebee's Avatar
bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 20,076
Mein Auto: 02 BMW 525i M54 auto 130K
Quote:
Originally Posted by G. P. Burdell View Post
Does an unrepaired, standard-length harness feel as if it is under tension when the trunk lid is all the way open?
I added four inches to mine so I can't tell myself.

I'll ask that question over in the E39 side of the house.
- E39 Electrical Problems Traced to Trunk Lid Harness Wire Chafing (DIY Diagnostic)

E46 owners can answer it here also.

PS: I think my DIY is more of the "how not to repair your trunk loom" because I flubbed up in a lot of places with ugly results!

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  #36  
Old 07-28-2011, 09:05 AM
bluebee's Avatar
bluebee bluebee is offline
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Location: San Jose, California
 
Join Date: Mar 2008
Posts: 20,076
Mein Auto: 02 BMW 525i M54 auto 130K
Quote:
Originally Posted by G. P. Burdell View Post
the problem is not that the wire harness is too short. The problem is the way in which the harness is designed to fold and unfold every time the trunk is opened and closed. All of that repeated flexing and exposure to heat and cold will cause the PVC wire insulation to crack and the strands of copper wire to break. Tension on the harness has nothing to do with it.
We've been collecting PICTURES of the broken wires, over time, over here:
Q: WHAT is the fundamental problem with the BMW wiring harness?

Just curious ... do you think these 'clues' support the excellent hypothesis above?


Last edited by bluebee; 07-28-2011 at 09:08 AM.
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  #37  
Old 07-28-2011, 10:04 AM
G. P. Burdell's Avatar
G. P. Burdell G. P. Burdell is offline
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Location: Southeastern U.S.
 
Join Date: Jan 2006
Posts: 1,734
Mein Auto: E46
Quote:
Originally Posted by bluebee View Post
Just curious ... do you think these 'clues' support the excellent hypothesis above?
Yes. PVC and other plastics, over time, lose their flexibility and crack. A short length of new wire doesn't always exhibit a lot of twisting in the wire strands.

If the problem is caused, as some have suggested, by excessive tension on a harness that's too short, then why do all of the wires seem to break at the same point? They're breaking there because that's where the bundle folds every time the trunk is opened and closed.

I think the more constructive question than "what's the mode of failure?" is "what's the practical way to fix it?" I hope my discussions of materials and methods have been helpful in this regard. The average 'Festers probably are a little bit curious as to why it happens, but they'd also like to fix the problem as efficiently as possible and go on with their lives.

Also, since we're in a thread I started, I'll give a brief update and say that the new wires are still going strong six months after I rebuilt the harness.

Last edited by G. P. Burdell; 07-28-2011 at 10:08 AM.
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Old 08-31-2011, 12:43 AM
TerraPhantm TerraPhantm is offline
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Bumping up an old thread: http://realoem.com/bmw/showparts.do?...37&hg=61&fg=10 is #3 a replacement harness for this? Or is that something else?

Thankfully my wires are still good, but I'd really rather not go through the trouble of rewiring it myself when the time does come. Any suggestions as to what can be done to relieve the stress?
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Old 08-31-2011, 07:01 AM
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G. P. Burdell G. P. Burdell is offline
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Quote:
Originally Posted by TerraPhantm View Post
Bumping up an old thread: http://realoem.com/bmw/showparts.do?...37&hg=61&fg=10 is #3 a replacement harness for this? Or is that something else?
I think that's the same part I asked our local dealer parts guy about, and he didn't think it was a replacement.

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Originally Posted by TerraPhantm View Post
Thankfully my wires are still good, but I'd really rather not go through the trouble of rewiring it myself when the time does come. Any suggestions as to what can be done to relieve the stress?
Short of never opening your trunk, I'm not sure that anything can be done to relieve the stress. The wires have to unfold and fold every time you open and close the trunk.

Last edited by G. P. Burdell; 08-31-2011 at 07:10 AM.
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Old 08-31-2011, 09:38 AM
johnrando johnrando is offline
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Since you can't relieve the stress, would it make sense just to wrap electrical tape over the wires to help reinforce them and help prevent rubbing?
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Old 08-31-2011, 10:29 AM
jcourcoul jcourcoul is offline
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That's why the maker uses fabric tape instead. Longer lasting and doesn't gum things up as bad as deteriorated vinyl tape.

All old cars develop the 'bad trunk harness wiring' sindrome. No escape. In my old Fords, I've had lasting success by wrapping the harness in rubber self-amalgamating tape. After a day or two, it fuses into a seamless rubber 'tube' that closely encases and protects the wires. The UK-made MotorMite brand I find at AutoZone is reasonably thin and doesn't increase harness diameter too much. Don't know if a harness wrapped like that could be teased thru the trunk access holes and rubber hose in the Bimmers.
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Old 08-31-2011, 05:38 PM
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G. P. Burdell G. P. Burdell is offline
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Quote:
Originally Posted by johnrando View Post
Since you can't relieve the stress, would it make sense just to wrap electrical tape over the wires to help reinforce them and help prevent rubbing?
Rubbing doesn't seem to be the problem; it's the flexing that weakens the individual wires in the bundle.

Quote:
Originally Posted by jcourcoul View Post
That's why the maker uses fabric tape instead. Longer lasting and doesn't gum things up as bad as deteriorated vinyl tape.
The fabric tape makes quite a mess, too, when its adhesive breaks down. Taking the old harness out and marking the wires was a sticky PITA.
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Old 11-18-2011, 11:35 PM
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Bump

I got this problem today!

Where do I start on this

This the wiring harnes on the right side?

How much would this cost me if I were to take it to a dealer or an independent mechanic?
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Old 11-19-2011, 06:10 AM
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G. P. Burdell G. P. Burdell is offline
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Quote:
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This the wiring harnes on the right side?
Yes.

Quote:
Originally Posted by Words View Post
How much would this cost me if I were to take it to a dealer or an independent mechanic?
I don't know. Having replaced the wire harness on my previous car, I never bothered to ask a dealer or my local independent.

If you get a repair quote from your local dealer, be sure to find out if they will replace the entire harness with a new one, or if they just plan to splice new wires into the existing harness. It's hard to tell from the parts diagrams whether there's a replacement harness available at a reasonable price.
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Old 11-19-2011, 07:04 AM
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I stickied this thread based on the potential hazard involved and that this is the type of thing that ought to be highlighted as the population of E46s ages (gracefully, of course. )

Hope that is ok with the OP.
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Old 11-19-2011, 09:41 AM
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G. P. Burdell G. P. Burdell is offline
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Hope that is ok with the OP.
No problem. I'm just happy to have created a thread worthy of sticky-ing.
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Old 11-19-2011, 07:23 PM
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So my first step is to open the black thing where the wires are and then see what wires went bad. Then what type of wire should I get at autozone?
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Old 11-20-2011, 06:02 AM
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G. P. Burdell G. P. Burdell is offline
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Then what type of wire should I get at autozone?
Local auto parts stores don't stock the wire you need for a lasting repair. My rebuilt wire harness is made from XLPVC-insulated wire sourced from McMaster-Carr.
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Old 03-09-2012, 01:59 PM
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On the way to work this morning, the trunk open indicator lit up on the dash. When I arrived at work, had to manually open the trunk with the key. I pulled open one end of the rubber cable cover on the wire harness in the trunk and saw that the brown wire was broken.

I think I'll just temporarily patch together the broken wire this weekend and start ordering the wire to build a replacement harness.
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Old 03-11-2012, 08:34 PM
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So did you patch it?

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