E39 Electrical Problems Traced to Trunk Lid Harness Wire Chafing (DIY Diagnostic)

For a cross reference, the other forum also has blue E39s with frayed trunk loom wiring problems causing errant open trunk messages.

- "trunk lid open"

Noticed the right license plate light on my 2001 black 540i was came on and stayed on after the trunk lid was opened then closed and noted if I squeezed the wiring loom with my fingers that the light would go on and off. After reading the info posted on Bimmerfest, I decided to pull back the trunk lid wire loom and found three (3) wires with that had the insulation separated and wires starting to come apart.

It didn't seem like the wires were being damaged by friction because there were no apparent signs of abrasion on the wire insulation and/or wires themselves; instead it looked like the wire insulation and wires were being 'pulled' apart. Anyway, I taped the three wires with electrical tape and then wrapped the entire wire bundle as much as I could with the boot pulled back as far as it would go. License plate light does not operate on it's own any more.

Not sure if I just transferred the stress to another spot on the wiring harness, but only time will tell. Sure do appreciate all the folks that contribute to this forum with their hard earned experience! This early heads-up has saved me much time, effort, and heartaches.

Originally Posted by calwilly1

it looked like the wire insulation and wires were being 'pulled' apart

I agree.

It looks like the wires are too short.

One potential solution, stated over in the E46 threads today, is to lengthen the wires, but not in the rubber loom itself - but to lengthen the wires inside the trunk lid.

That might work (too bad I lengthened mine inside the rubber loom itself). Mine looks like a royal mess!

Here is the reference in the E46 forums:
- PSA: Check Your Trunk Wire Harness

We never did find out what wires #2 and #13 innervate, nor what problems occur when those parts are enervated.

Does anyone know what wires #2 (red/black) and #13 (brown/blue) go to?

This thread today, where the guy couldn't read the warning due to pixels being out, got me thinking of posting the error message that occurs when the trunk is open and/or when the licence plate light is out due to worn or frayed or broken or shorting BMW ED39 trunk loom wires.
- Wtf is this error?

Here is a shot, re-used from this thread, of the two errors I got when my trunk loom wires were acting up:

There was an excellent DIY posted today where a 3-series driver "rebuilt" his trunk wiring loom and posted the step-by-step details how to do so.

Read this:
- PSA: Check Your Trunk Wire Harness (post #31)

As for the wires, does anyone know what gauge they are?

Answer is here:

18- and 20-gauge wire

To those who have not yet modified their trunk loom - would you run a test for us?

We don't know if the "problem" is that the wire is kinking, or that it's being pulled apart.

One way to tell, as suggested here, is to see if an unmodified loom is under "tension" when the trunk is in the fully open position.

Q: Is your trunk loom in tension with the trunk fully open?

Originally Posted by bluebee

To those who have not yet modified their trunk loom - would you run a test for us?

We don't know if the "problem" is that the wire is kinking, or that it's being pulled apart.

One way to tell, as suggested here, is to see if an unmodified loom is under "tension" when the trunk is in the fully open position.

Q: Is your trunk loom in tension with the trunk fully open?

On my 540, the loom isn't under tension, and when I close the trunk, I can't see any sign of pinching or kinking, nor do I see any signs of wear and tear on the boot.

My trunk has just begun spontaneously opening and I've traced the issue to the wiring loom.

I've read this entire thread and cringed when I saw how BB cut apart her rubber scuba hose. In the Bentley manual it shows how to remove the inner trunk cover (i.e. the piece with the toolkit in it) and then unplug the harness from the three connectors, and pull it out through the hole where the scuba hose attaches to the trunk lid. Then you can work on the harness relatively easily with it out of the trunklid.

That's what I plan to do since my wires are not obviously frayed under the scuba hose. More later, I suppose...

Originally Posted by Spencercat

cringed when I saw how BB cut apart her rubber scuba hose. In the Bentley manual it shows how to remove

I didn't know any better!

And, I didn't even think to look in my Bentleys!

Is this the section you're referring to?

• 2002 5-Series Bentley, page 412-2 "Trunk Lid, Tailgate" (pg. 830)

If so, you see "more" there than I do!

I couldn't possibly get the wiring harness out from just that!

When you do this, please post back a few pictures so the NEXT person stands on your shoulders!

Just got back in from diagnosing my problem. Long story short, my buddy and I didn't find any problems with the wiring. Or maybe that should be The Bentley instructions are pretty clear - remove the three connectors (actually four since the license plate lights each have their own) and the wiring harness can be pulled out where the scuba hose ties it into the car.

I pulled the harness through that hole about 8 inches, and pushed back the sock covering the harness (and also moved the scuba hose) but found nothing but new-looking wires. No chafing, no broken wires, nothing. Replaced some of the old tape that I pulled off and reattached the connectors, etc.

We continued undaunted to check the switch next to the hood release (nothing happened when we jiggled it). Then we located the relay under the glove box. After wrestling to get the white box out from under the glove box, we wired it up and "tested" it by shaking it around to find if there was a loose connection. Nothing.

Then we went on to the key lock on the trunk. No dice there since the key opens the lock mechanically. The wire from the key lock simply connect it up to the door locks (who opens their door locks from the trunk lid?).

I guess I will find out soon enough if we solved the issue by reconnecting something when I drive the car next. Either that or I will try a new key battery per someone else's guess earlier in this thread...

Originally Posted by Spencercat

The Bentley instructions are pretty clear - remove the three connectors (actually four since the license plate lights each have their own) and the wiring harness can be pulled out where the scuba hose ties it into the car.

Thanks for the clarification on how to remove the harness.

I think a LOT of us would have done that had we known it was so "easy".

In fact, some of us think the problem is that the harness is about an inch too short (the wires appear, in some cases, to be pulled apart), so your entire-harness technique allows for a lengthening of the entire harness.

Originally Posted by Spencercat

I will try a new key battery per someone else's guess earlier in this thread...

I never tried it; but, these may give you a head start:
- BMW diamond key initializing (1) (2), opening, charging, recoding, & battery replacement (1) (2) (3) (4) (5) (6) & converting 1996-2000 "square" key to a diamond key (1)

For cross reference, in a thread today, the classic symptoms were displayed:
- Central Locking system stopped working

Originally Posted by stevenhussey

What and where is the trunk loom? My 540 tells me all the time that my trunks opened, check lic. plate lights and the trunk lights always on when im in it. and the trunk only opens with the key.

The symptoms listed by stevenhussey are about as classic as they get for a frayed trunk wiring loom.

I asked him, over in that thread, to help us ascertain if the wires are being "stretched" to the point of failure or if they're being "bent" to the point of failure; and I asked him to snap some before & after pictures to expand our tribal knowledge in this classic design problem.

A few weeks have gone by since I partially removed the trunk wiring harness to check it for breaks. I have not had any more trunk opening incidents. I guess moving things around did the trick for me.

For the future record, we've had another satisfied user who had his trunk loom repaired by an indy, which fixed the LICPLATE LIGHT and other gremlins we've described here.

More details in this thread opened today:
- trunk wiring harness

Originally Posted by Nubbiess

I remember seeing a thread on this topic somewhere, but I can't locate it now. Anyhow I was having a problem with my license plate lights on a 2002 525i where the light was inoperable when the trunk was closed, but once the trunk was fully extended it would work fine. I had a local Indy (Micro Motors) take a look at it and they found the problem was in the trunk wiring harness and repaired it for $75.

Anyhow, just wanted to let everyone know that the grey and brown wires were the culprits and that they controlled the left side license plate light.

For the cross-link record, specifically for the LICPLATE light (which has other issues), see also:
- Trunklid open, check licplate light, and other trunk wiring loom woes (1) (2) (3)

Looks like the mechanic added the extra layer of plastic to each of the wires in the harness, but after removing the electrical tape I still see some nicks on the wire.

I wrapped up the nicked wire, but the next time something electrical goes wrong I will know which color wire is most likely responsible.

Originally Posted by Nubbiess

the mechanic added the extra layer of plastic to each of the wires in the harness

Thank you very much for the update as you're the FIRST person to snap a picture of a professionally-repaired trunk loom!

It's very interesting to see 'how' the pros attacked the job!

Thanks for giving back to the team!

Third brake light is now out. Not sure if it is related to the trunk harness but will update when I know more.

Originally Posted by Nubbiess

Third brake light is now out. Not sure if it is related to the trunk harness but will update when I know more.

Update?

Anyway, for the cross-link record, today, over here, a frayed loom caused one of us to replace the actuator (which didn't work at first 'cuz the actuator wasn't the problem!):
- Trunk stuck...

Originally Posted by [URL="http://www.bimmerfest.com/forums/member.php?u=165177"

izquierdo[/URL]]That's exactly what my problem was. Except not to that extent. I had one wire completely severed and two other wires with the insulation ripped exposing the copper strands. I fixed the three and all is good now.

I did check [the loom] before I bought the actuator and everything seemed to be fine. But I didn't pull the protective rubber down far enough to actually see the severed wire until I installed the new one and realized it still didn't work and pulled it down even further for another look. Oh well, you live and you learn.

Looks like more than a few people have a 'stuck trunk' that can be traced to the trunk wiring loom being frayed:
- E39 (1997 - 2003) > Trunk stuck...

Originally Posted by Jimmys 530i

I had the same problem with my 530i, but 5 wires were severed.

Call me bat-sh*t crazy, but wouldn't plain old butt-end crimp connectors solve this problem a lot quicker, easier and cheaper than any of the aforementioned? Got a silver '01 525i with five frayed wires in the trunk loom - causing relatively minor problems (trunk open warning, maybe a fault code, but I haven't scanned). I'm going to give these a run and see how it goes... I can always come back to soldering if need be.

Originally Posted by bluebee

Answer is here:


To those who have not yet modified their trunk loom - would you run a test for us?

We don't know if the "problem" is that the wire is kinking, or that it's being pulled apart.

One way to tell, as suggested here, is to see if an unmodified loom is under "tension" when the trunk is in the fully open position.

Q: Is your trunk loom in tension with the trunk fully open?

I am curious as to where the stress point is on these wires?
I get the sporadic brake lights warning on board right after ignition and goes away after a few seconds. The light bulbs were working fine every time i checked so i think i'm "joining the club"
I watched as the trunk lid opens and closes a few times to see how that snorkel behaves. It looks to me that the stress point is right after the exit form the trunk lid, as the snorkel is forced against the car body and makes almost a 90 degree bend (when the lid's closed). If that's the case, maybe reinforcing that point with a 90 degree angle could solve the problem.
It's really hard to tell from the photos whether all the wires get broken in the same area as i think some have pulled the harness out of the trunk lid a little bit.
Can this be confirmed by those who opened the snorkel? I haven't cut open my snorkel yet, as the problems i get are so sporadic and i haven't figured out a solution.

Originally Posted by bmwbmc

It looks to me that the stress point is right after the exit form the trunk lid, as the snorkel is forced against the car body and makes almost a 90 degree bend (when the lid's closed).

That's exactly where all my wires were frayed and/or broken!

Originally Posted by bmwbmc

maybe reinforcing that point with a 90 degree angle could solve the problem.

I hazarded a guess that the loom was stretched at that point (hence a 'fix' would be longer wires), but, I think your idea is aimed more at the problem than mine was.

Originally Posted by bmwbmc

Can this be confirmed by those who opened the snorkel? I haven't cut open my snorkel yet, as the problems i get are so sporadic and i haven't figured out a solution.

You 'can' just pull the snorkel down from where it connects with the trunk lid. That's how I originally found my severed and frayed wires.

Still - I second the notion that the NEXT person with this problem please try to identify, before you modify things as we did, WHAT is causing the wires to chafe and fray.

I wrap harnesses prone to breakage snugly with a stout friction tape after repair, it forces them to flex as a bundle and eliminates the stress falling on a single point which will fail sooner.

Before


After


Tape Used(enlarged to show part number)