HOW TO: Repair and Modify Damaged W203/C203/CL203 Door Mirror Loom/Frame

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Active Member
Oct 31, 2010
2005 C350 Coupe SE
ok, so I made this repair a long time ago, and simply forgot to compile this how to guide, so here goes and hopefully it'll be of some use to someone in the future.

Couple of points to note before I get started

My mirror frames and wiring are different per side as is standard, however I have a left hand drive n/s frame so that i can have the dimming function as well, and the frame I bought has the wiring for memory as well, your car will likely have different configurations between the two sides, but unlike mine, you'll have less wiring on the n/s not more!
  • You'll need a fair bit of patience to do this and basic skills
  • Tools required will be a soldering iron, wire working tools, small file or dremel type tool, small pieces of metal and something to shape them with, and likely a 5 point torx tool/set to remove the frame from the car.
  • You will need some small lengths of wiring of a similar type/rating or heavier duty, don't go smaller, colour is not important so long as you note what goes to what!
  • You'll also need some sort of cable wrap/heat-shrink or something similar, you'll get the idea from the pictures and as you look at it yourself.
  • Some of the pictures might switch between left/right side as we go through, this is simply because i did both sides, and took pictures as i went, and used the best ones to show each stage.

Firstly, lets have a look at the problem....
  • Your door mirrors have stopped:
  • moving/adjusting
  • defrosting
  • folding
  • Indicator failed (and not caused by the LED unit/Bulbs failing)

These are all indications of this problem, although of course it could also be the switch pack or other wiring issue, so first thing to do is remove the cover and have a look (this is done by folding the mirror in and using a flat blade screwdriver to release the cover clip and slide the cover off, you may need to push the mirror manually in at the hinge end to allow the cover to slide off, the process can be seen here

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Now lets see if you are likely to have this problem, in the images you can see the problems highlighted.

Picture 1 - excessive bend is visible with damage to the wiring wrap, after you remove the mirror and unplug this loom you will notice it's really weak at this point, and hinges where cable breaks are

Pictures 2 through 4 - show the same bend that is the problem. (image 2 also shows the heating element wires, also crimped by bad placement when fitting the glass)

Pictures 5 through 8 - show the wiring with the mirror frame in various stages of folded, and you can see the toothed gear arm in close proximity to the loom

Pictures 9 and 10 - show what that toothed arm does to the loom wrapping

At this point if you are sure the problem lies in the frame wiring, you're going to want to remove the whole mirror unit from tthe car, it would be a lot harder to fix in situe, i'm not going to go into that process here, lots of videos on you tube for that if you can't work it out, beware of the likely need for a 5 point torx-plus drive bit to remove the frame from the car, unless you've had a helpful garage change it in the past and put regular allen key headed bolts in there when putting it back (PCS - thank you ollie)

So, once you have it off the car and start stripping it down, the problem becomes very obvious!

Pictures 11 + 12 - not so obvious in the image, but the cable may be broken at the arrowed points and when you hold it and flex it, it 'hinges' rather than bends in a loop

Picture 13.... ah the one that was literally sawed in half!! only thing holding that together i think was one wire and the fabric wrap!

Once you've removed all the sticky fabric crap they wrap their looms in (it does serve a purpose other than to annoy you when removing it! it supports the wiring whilst allowing it to flex some unlike heat shrink, although it doesn't do a great job) you'll need to work out where to cut the wiring back to, if you can, it's best to stagger the joints, however, things like space restrictions, number of wires and position of the damage will restrict your options.

End of Part 1 (had to break it up because of the limit of 20 images per post :rolleyes:)
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Part 2......

Now it's time to work out where to route the cable so this problem doesn't happen again, because unless you plan on replacing all of the loom wiring, you're going to need joints somewhere to add in extra cable length, and these will take up more space and be less flexible, the exact position the joints and routing of your cables are going to depend on the exact position of the damage you have, mine was similar for both and thus the re-routing was similar, i think the only difference i had was one of the frames I did not use the original cable guide/clip because it caused a point at which the cable was again folded at due to it's fixing and the size of the loom given the extra features wiring, and my plan/design calls for the cable loom to be looser and freer to move.

Picture 1 - here you can see I've cut back to remove all of the damaged areas, in this one I've cut everything together mainly because i didn't get much of a chance as it got chopped by the toothed arm, I tried later to stagger the joints a little.

Picture 2 - shows one soldered neatly together, i did them side by side to reduce bulk, be sure to use a small emery board after to remove any slight sharpness as little points will work their way through insulation and short out the loom later.

Picture 3 - shows the heat shrink insulation i used, i had a few different things in mind for this, but 2 layers of heat shrink provides the best support, initially i overlapped the heat-shrink over the original insulation for strength reasons, i think on later ones i might have made the first layer the exact size of the joint and then used the top layer to overlap the whole area. (when doing the second set of joints on a wire, don't forget to put the heat-shrink on the wire first!!)

Picture 4 - part way through after a couple repaired. (different coloured heat-shrink is just down to what i had and the size it was and the wires i used, some were thicker than others)

Pictures 5 and 6 - show this section of the loom joined to the new wires and me adjusting how it all sits together.

Pictures 7 through 9 - show me just sorting out a possible route, taking into account the wires needed for the glass dimming and heating. and you can see where the joints move to when the mirror is in the folded position.

Picture 10 - this is the 2 wires for the indicator unit, these too are a problem for breakage, so here i've decided to heat shrink them to make them more rigid, in the hopes that the folding motion will then push the cable through it's access hole, rather than fold it up and snap the wires

Pictures 11 and 12 - here you can see me working out where to start cutting the wires to length and re-joining them, with the heat-shrink on the cables ready to put in place after the joints have been soldered and cleaned and de-burred!

Picture 13 - visible in picture 12 above, this is the mesh sleeving i used to re-wrap the cable loom, the more you stretch it, the smaller it gets and thus keeps the cables together, it's particularly useful in these types of scenarios, and can be slid on and bunched up out of the way and taped there till you're ready to stretch it the full length of the loom.

Pictures 14 and 15 - this is the new section of loom being connected to the plug section, used a slightly different heat shrink layering method here, i think it was better, I also had much more scope for staggering the joints as you can see in 15 once all are re-joined.

Pictures 16 through 19 - completed repair with the sleeve stretched out and taped at each end and refitted to the mirror movement motor

Picture 20 - this shows the repaired cable loom with the mirror mounting and movement motor lifted off, as you can see I split the loom into 3 nearly as soon as i could. You can see the straight cable at the top, this is the indicator cable, and as it turns out even using the heat shrink to stiffen it didn't fix the problem completely, fix will be detailed in the next section. Also, you can see that for the first section covering the first repair joints, i've used heat-shrink to make it stiffer and resist the temptation to kink when the mirror is in the normal use position, this was important to ensure he cable slid/moved where i wanted it to

End of Part 2
So, having repaired your loom, and as you can see from the images I've already posted, we're going to take a completely different route to the motor socket, utilising all of the space inside the cover to allow the cable loom to expand out into which should work quite well, that just leaves the indicator wiring, which originally also had an issue with it folding where you didn't want it to, and being restricted/tied to the other loom, so the plan was to stiffen it, and force it to slide through the hole and utilise the space at the back of the mirror mounting frame to move freely in - yeah, good idea in theory, in practice the dam cable still snagged the edges of the hole, and caused it to fold up badly.

Part 3.....

So, here's the fix.

In the last picture in the loom repair section (#20) in the previous post, you can see the original profile of the cable hole, and i'd labelled it as a problem area, what you can't see too well from that image is the hole is at the top of a sloped section, so, what i did was elongate that hole into the slope, thus the cable would then move freely into the hole rather than rubbing on the edges as it was forced to do originally.

Pictures 1 and 2 - show the hole elongated into that sloped area

Picture 3 - this was the same thing from the frame for the other side of the car.

Picture 4 - this is the mod finished with a little bit of paint to stop any corrosion of the alloy

Pictures 5 and 6 - these are from the other side of the frame showing the elongation of the hole.

Pictures 7 and 8 - these show the wiring from the back side of the frame to the indicator unit plug, and shows how i taped it in place, the difference between the 2 is how the cable behaves between the folded and non folded frame state.

Picture 9 - is from the frame on the other side of the car.

At this point there was still the occasional tendency for the indicator cable to not go where i wanted it, so i made a small plate to 'guide' it, using the original useless cable guide post to locate it and a small screw to secure it, this plate is shown in these final 4 pictures, in the last 3 you can see where I shaped the edge of it to ensure the cable did not snag during movement.

End of Part 3
Part 4 (and final part).....

So, there we have it, fully working 203 model C-Class mirror frames that won't break if you set them to auto fold on locking, just some final shots of the repair/modification once complete, and once back on the car, with the frame in folded and normal positions and as you can see, no more nasty bends or other issues.

Just one final point, for some reason stupid PostImage upload site decided to rotate 90% of the images to the right by 90 degrees, no idea why it saw fit to do that, and i can't be bothered to go back and fix all of them, I've done the ones with text on them.
Having just read back through my posts above, I need to stress one thing, when sizing the new loom length, make sure the mirror frame is in the folded position, because its in that position that all the slack is taken up, and the full length of the loom is required.
Given this is the second reply I've had to make adding extra info shows why, you should always do these types of threads right away while stuff is still fresh in your mind :wallbash:

Someone asked me about the indicator cables changing colour/stripe colours, and did I have to lengthen them?........ good question, well presented, and after i'd rattled my memory for the answer :rolleyes:........ I think I made reference somewhere in the guide above about the indicator wires also being subject to having a tendency to fold and break, and at least one side had suffered this fate, the other i fail to remember, but I do think I did extended them slightly to assist in the routing and flexing method I wanted, given it's a fairly easy thing to do having just done the same on all the wires from the other section of the loom.
Having just read back through my posts above, I need to stress one thing, when sizing the new loom length, make sure the mirror frame is in the folded position, because its in that position that all the slack is taken up, and the full length of the loom is required.
Duration from part 1 to part 4?
Duration from part 1 to part 4?

So it seems that there was a period when i wasn't getting reply notifications, so my reply now is probably of no use to you being so slow/late (sorry) but for others it may be.

assuming you have all the parts sourced and to hand (wire, sleeving, little piece of metal for the guide plate, tools, soldering iron, heat shrink etc) I think it took me a few days/evenings, I think you could consider it a weekend project, but, if you were to go at it first thing and crack on you could have it apart/fixed and back together by that same evening i guess
Some of the frame wires are all black too so difficult to repair if you don't know which joins to which. We extend the wires so the soldered joint wont be in the flex position. The repair can last if the mirrors are not folded much.
I think i was fortunate in the colour department, but yeah, if all black that's a pain.
getting the repairs into a non-bending area i found impossible with the number involved, so had to come up with that re-route idea, especially as i wanted to use them more than a few times before the armature sawed it's way through the loom again!

You did tell me that enabling the auto fold would cause me headaches 🫣 it did surprise me how fast that happened though. :wallbash:

Fix currently still working fine, only issue i have is the passenger side indicator likes to stop occasionally, then start again a couple of flashes after operation starts lol... i think that's the stupid little socket fixing, as that side wasn't the most secure and when initially refitting the cover it didn't line up correctly, and when it did i'm not convinced it fully engaged, i'm not bothered, if it gets worse, i'll take it apart and fit the smoked "audi" style tracer units i have, they have fly-leads and you connect them before pushing the cover into place.

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