PSA: Check Your Trunk Wire Harness

Didn't have a chance to make the repair this weekend. It appears that the brown wire is the ground for the interior trunk lights and the automatic trunk release. I just covered the bare ends of the wire with electrical tape to prevent anything from happening. I'll fix this next week sometime.

I fix mine with eletrical tape and the light went off and everything works


but now on my Dash, it tells me my license plates lights are out.

Could this be because of the wiring trunk harnes(meaning part of the trunk cables are affiliated with the license plate lights?


PS where can I buy LED license plates ???

Originally Posted by Words

but now on my Dash, it tells me my license plates lights are out.

Could this be because of the wiring trunk harnes(meaning part of the trunk cables are affiliated with the license plate lights?

The trunk wire harness supplies power to all of the electrical devices in the trunk lid, so yes, there are wires for the license plate lights in that harness.

First things first - have you checked to make sure the bulbs light up and the contacts are clean?

You may want to revisit your repair job in the near future; electrical tape has a tendency to unravel as the adhesive degrades.

Well there was one light brown cable that cut in half, so I spliced it.

But before I did all this, one of my license plate was out. When I spliced it... I didn't get no warnings until two or three days later. At first before I fixed the wiring harness, the red lights would come on and the go off after 2 minutes. But now they are on until the car is turned off.

Is there a tutorial on how to remove the license plates lights?

Or how to check to see if the are working properly(I was going to get some LEDs, but there is no point if the cable are bad)

Sigh...

Originally Posted by Words

Or how to check to see if the are working properly(I was going to get some LEDs, but there is no point if the cable are bad)

Sigh...

I would imagine that you could remove the bulb and check the continuity to see if the bulb has burnt out.

On my trunk, the brown wire broke and I found a couple of the other wires are starting to break. I picked up some wire and I'm planning on repairing this tomorrow. I'm just going to replace the bad wires by replacing the section that runs between the trunk and the trunk lid and splicing in a new wire.

I hope I can get away with only replacing a couple of wires now and that will be it.

I have an e46 (2000-328i) and have been dealing with this issue for a while now. About every 3 to 6 months I have pull out my fire-starter soldering iron and just solder the wires back together. This is starting to get tiring. I'm curious about the success of the following:

1) Has anyone replaced the complete wiring harness with a non-home-made (like GP) one?
2) Has anyone replaced individual wires (the whole length). I.e. a single ground wire from end-to-end?
3) Has anyone found correct color-coded wire spools (ie. Blue with the yellow stripe)

GP, when you rebuilt your wire-harness did you use color-coded wires? If not, how do you anticipate repairing split wires ten-years from now (for the sake of argument, let's assume you'll keep this car forever)?

Thanks for any input, info and help anyone can provide.

I will post some pictures of my repair job and explain what I did soon. I will also try to trace through the wiring (I have a Bentley Manual for the e46) and post that soon also.

;-> (consternation)

Originally Posted by consternation

2) Has anyone replaced individual wires (the whole length). I.e. a single ground wire from end-to-end?

Some of the wires originate from the General Module or the Light Control Module in the dash; it would be a major effort to replace the entire run.

Originally Posted by consternation

GP, when you rebuilt your wire-harness did you use color-coded wires? If not, how do you anticipate repairing split wires ten-years from now (for the sake of argument, let's assume you'll keep this car forever)?

I color-coded the wires to a certain extent. I could have used many more wire colors than I did, but with the ordering minimums at McMaster-Carr, I would have wound up with a lot of excess wire when I was finished. Brown insulation wasn't available for ground wires, so I used black for all of the grounds. I think I used five different colors.

If I should ever have to redo the job, it should be made a little easier by the numbered wire markers I attached to each wire at the connectors and at the splices in the trunk...assuming the markers don't fall off when I open things up.

Originally Posted by consternation

3) Has anyone found correct color-coded wire spools (ie. Blue with the yellow stripe)

I neglected to answer this question earlier. I was not able to find the exact colors and stripes of the wires in the harness, but I admit that I did not spend much time trying to match them. I suppose I could have located them if I looked hard enough, but my top priority was to repair the damage before it got worse. Had I found the exact matches somewhere, I suspect that the ordering minimum for the exact match for each wire would have been prohibitively expensive. The minimums at McMaster are relatively small, and if you mark the wires and keep good notes, you'll have a good reference if you ever need to get back into the harness later.

If you plan on replacing the wire harness with a homemade one, just use as many solid colors as is practical for your budget.

GP, a small question, instead of routing through the existing hole below the rear window, is it not possible to route the wires so they come from inside the trunk area to the trunk lid and use a plastic loom to keep them all together so there would not be so much tension on the harness, this would allow you to splice in extra length and it would just hang down in the trunk, just a thought

Originally Posted by vintagez

GP, a small question, instead of routing through the existing hole below the rear window, is it not possible to route the wires so they come from inside the trunk area to the trunk lid and use a plastic loom to keep them all together so there would not be so much tension on the harness, this would allow you to splice in extra length and it would just hang down in the trunk, just a thought

I suppose it would be technically feasible as long as the harness is properly supported and protected, and the passthroughs in the trunk lid and body are sealed. However, I'm a stickler for making repairs and modifications that look stock and, more importantly, don't introduce potential problems. The factory harness routing puts all of the wire behind the carpeted panel on the right side of the trunk. Objects in the trunk would snag an exposed harness and damage it, and its appearance would also turn away potential buyers who know what the stock harness routing should look like. Some might consider it a hack job and look for another car.

Running a new harness along the same route as the stock harness, with more durable wire, would be the better choice from aesthetic and functional standpoints.

Thank you for the excellent write-up on this. I wouldn't have thought to trace out the whole harness, but if you're going to do a job right...

I went to the McMasters-Carr website and was overwhelmed at the variety of wire available there. You wouldn't happen to have the item numbers and length of wire you purchased available? They say imitation is the finest form of flattery.

Originally Posted by ChiefAndy

I went to the McMasters-Carr website and was overwhelmed at the variety of wire available there. You wouldn't happen to have the item numbers and length of wire you purchased available?

Thanks for the compliments. You can narrow your McMaster search to crosslinked-PVC-insulated (XLPVC) wire by selecting "UL 1429" under the "Type" heading in the left sidebar. Then you can select the gauges and colors you want. Choose as many colors as makes sense to you when you rebuild your car's wire harness.

Good luck!

Thanks for the quick reply. Tomorrow, it's back out to the car to see how many wires are 18 guage and how many are 20. Searching that way made it easy!

You forgot to mention how the wiring fried

Ps

the way I splice my cables has worked fine as of today. I replaced my license plates lights and have been working fine.

Thanks for this thread as it's given me a good starting place for my Problem. I have a 318Ti and the boot (trunk) lid won't stay shut. Every time we close it, you hear the automatic release mechanism activate and unlock it again. Only once the car is fully locked will the boot stay properly shut. We are having to drive the car at the moment with the warning light on on the dashboard and witht eh boot lid only shut on it's safety catch.

It certainly seems to be a short circuit as the problem has got increasingly worse over the last couple of weeks.

R

Temptations are a motha****a who says you can work on cars while having fun with the ladies. bench press and drink some beers. on the side

Thank you for this informative posting because I too am now dealing with this problem. I've decided to avoid the frustration and just replace the entire loom at $500. But what I want to know is whether or not the wire loom comes with a new rubber hood or if that is a separate purchase? I can not find a separate rubber hood on RealOEM and the parts stores that sell this piece (61126919968) do not know if the rubber hood is with it or not. Thanks for the help!

Originally Posted by JRod4U

Thank you for this informative posting because I too am now dealing with this problem. I've decided to avoid the frustration and just replace the entire loom at $500. But what I want to know is whether or not the wire loom comes with a new rubber hood or if that is a separate purchase? I can not find a separate rubber hood on RealOEM and the parts stores that sell this piece (61126919968) do not know if the rubber hood is with it or not. Thanks for the help!

Have you confirmed that the part number is for a complete replacement trunk lid harness? My local dealer parts guy wasn't able to do so, and I didn't want to gamble $500 on a special-ordered electrical part that I couldn't return.

I talked to three sellers of the part with that number given to them. They tell me that is the correct harness for my 2001 (March) 330i. But nobody can tell me if the hood is part of it. The best they can do is tell me that they do not find the hood listed separately in the diagrams or catalogues.

You know, I kept wondering why this thread continued to be a sticky for so long, until I was a victim...

Anyway, I need to go in and splice a couple of wires (driver trunk release button not working and getting an intermitent dash warning light that I've got a rear brake light bulb out). Questions:

1 - When I get to the wires, do I need a gauge measurement tool to determine gauge of the specific wires I need to splice?
2 - I need to keep the rubber boot in tact I assume since I'm not replacing the entire loom, i.e. it is one solid rubber tube?
3 - If I'm just splicing, should I go with the recommended XLPVC replacement wire or should I select something more in line with the OEM wiring I am splicing within? Or will either work just fine?

Originally Posted by delirium330

1 - When I get to the wires, do I need a gauge measurement tool to determine gauge of the specific wires I need to splice?

If you have a caliper, you can use it to measure the diameter of the bare wire and then compare the measurement to the values in a wire gauge table.

Originally Posted by delirium330

2 - I need to keep the rubber boot in tact I assume since I'm not replacing the entire loom, i.e. it is one solid rubber tube?

It's one continuous corrugated tube. To replace a cut or damaged boot, you would have to cut the wire harness inside the car, thread it through the new one, and re-splice all of the wires.

Originally Posted by delirium330

3 - If I'm just splicing, should I go with the recommended XLPVC replacement wire or should I select something more in line with the OEM wiring I am splicing within? Or will either work just fine?

I haven't taken a close look at my two-year-old XLPVC wire harness, so for now, I'll just say that XLPVC or a quality (read: not the cheap auto parts store stuff) PVC- or XLPE-insulated wire should make for a good repair that, depending on proper splicing technique, climate, and usage, should last for a few years.

Be aware of the wire vendor's minimum quantities if you order by mail.

Originally Posted by delirium330

do I need a gauge measurement tool

I see you have an answer from the expert already - but - if it helps, we've on the E39 side determined the gauge of all the wires, which you'll find in this thread.
- How to diagnose & repair cracked, broken, or frayed BMW trunk loom wires causing all sorts of strange mischief (1)

I don't know if the E46 gauge is the same - but - the PROCESS we used to determine it should be the same.
I suggest that the NEXT person who repairs the loom, report back to the team what the respective E46 wire diameters are, so that everyone who follows stands on your shoulders.

Here are the answers for the E39 (which may be similar for the E46):

Originally Posted by delirium330

should I go with the recommended XLPVC replacement wire

There is a recent healthy discussion of what material to use for the BMW trunk loom in the alt.autos.bmw USENET nntp newsgroup, which you can find over here:
- What is the root of this BMW design flaw in all 3,5,7 series BMW trunk wiring looms?

Note: Google stinks as a nntp newsreader - but I give the Google Groups link because some of you might not have an NNTP protocol client installed.

EDIT: (didn't see this when I had posted above)

Originally Posted by JRod4U

But nobody can tell me if the hood is part of it. The best they can do is tell me that they do not find the hood listed separately in the diagrams or catalogues.

Most of the time, when I call the stealer, the data matches - but - for some whacko odd reason, all the answers I received from calling MULTIPLE dealers on the trunk wiring loom make no logical sense.
You would think that the dealer would be VERY FAMILIAR with the trunk wiring loom part number - since a LOT of people MUST be going to the dealer to get their strange electrical symptoms fixed - and I can't imagine that the dealer is manually splicing wires like we do.
So, logically, there must be a LOT of trunk looms being replaced, right?

Guess what? I called BMW of San Jose, BMW of Mountainview, and BMW of Fremont (my three closest dealers), and NONE said it was a commonly replaced part. In fact, none had the wiring loom in stock. And, all professed total ignorance of anyone ever ordering a replacement loom.

This makes no logical sense, I agree. So, anything you can find out by calling the dealer, and reporting back, would be useful information for both the E46 and E39 teams!

Where is your wiring splice coming from dude?

Originally Posted by G. P. Burdell

If you have a caliper, you can use it to measure the diameter of the bare wire and then compare the measurement to the values in a wire gauge table.


It's one continuous corrugated tube. To replace a cut or damaged boot, you would have to cut the wire harness inside the car, thread it through the new one, and re-splice all of the wires.


I haven't taken a close look at my two-year-old XLPVC wire harness, so for now, I'll just say that XLPVC or a quality (read: not the cheap auto parts store stuff) PVC- or XLPE-insulated wire should make for a good repair that, depending on proper splicing technique, climate, and usage, should last for a few years.

Be aware of the wire vendor's minimum quantities if you order by mail.

Thanks GP and Blubee, just put in an order at McMaster-Carr. Got 2 colors in 25ft length to just patch up the bad wires for now. For others reference, it was about $7 per 25ft length of the UL1429. I'm enticed to do the full repair, but I just did a brake/rotor job 2 weeks ago and I don't have the gusto for an all afternoon splice session.

EDIT: Before you order wire to do this repair (if the only sympton is the driver footwell trunk release not working) check that the valet security isn't on by turning the trunk unlock manually. Doh!