Aviators

Hi,

Have read many of the threads on here regarding pulling apart the left side of the trunk and finding a break in the 3 wires running from the trunk close/lock switch that break due to flexing over time.

I can't find a break in these, haven't pulled off all the wire ties but have spent 20 min looking.

Tested the switch w/ a micrometer in hundreths Ohms setting - no resistance until button pushed, then resistance. Don't know if this means the switch isn't faulty (electrical isn't my forte) - but thought I'd mention.

NOTE - the switch inside the car by the driver's side footwell will open/close the trunk.

I've concluded due to this the motor is fine but it's either the switch or a wire break (or something else?)

Any thoughts before I throw it all back together only to be right where I started?

Thanks much!

vietjdmboi

how did you conclude the motor is fine?

are you getting power at the motor connector when the button is pressed?
make sure you do this with the trunk at different heights to replicate it opening/closing
if you do, the switch should be fine.

to check the wiring, put the voltmeter on continuity and put one lead at the connector and the other end as far back as possible. wiggle the harness slowly to see if continuity goes away.

hope that helps.

Aviators

My thought re: motor being fine was that I can open and then close the trunk via the power mechanism from inside the car (switch down by doorsill).

Don't have a continuity mode on this meter- will see how to do that but didn't realize that could be done on the outside of wire insulation. Thank you for the explanation!

Cheers

vietjdmboi

you can use the ohm setting. wiring has a resistance unless there is a break. you will need to backprobe the wire to make it possible.

Aviators

Thanks again for your reply.

Turns out I did manage to find the cuts. All 3 trunk button wires cleanly severed, with 2 more cut through the insulation and a number of strands ready to fail any day.

I looked everywhere except for removing the tape right at the top where the plastic wire loom/protector begins, and sure enough it was cut right beneath there.

How nice to have working buttons again!

Cheers

Dublinoh

Replying to this thread for those who don't know about the wire loom issue. Apparently this is a very common failure which effects auto-trunk feature and license plate lights among others. I fixed this yesterday and the brown ground wire was broken right where it enters the plastic sleeve near the back of the hinge (drivers side). I cut a zip tie and cut the sleeve back about two inches and could then see the break. As soon as I connected the severed wire the trunk lights came on etc.. You can search for more complete instructions but this is very doable for even the not so mechanically inclined.

tumbler510

What's the fix? A simple splice and addition of some wire to bridge the gap?

tlambert

Yup pretty much.

Mine was the same. It would open from the switch in the door but not at the trunk.

I don't remember how many wires are attached to the left hinge (a lot!) but the majority of mine were either broken, about to break, or previously (poorly) repaired.

I pulled all the electrical tape off from that harness to the floor. I cut each wire one at a time. Added new wire 2in longer for each wire. The reason for making them longer is they come out the back of the plastic hinge cover and get bent/broken making that bend going down. I hope having a bigger loop will not make it bend so sharpe going towards the floor.

Soldered and heat shrink on each splice. Yes that's twice per wire...which bites while sitting and leaning into the trunk.
I taped the harness and added a couple of zip ties to support it at the back part of the hinge.
I also had 2 koax wires for my satilite radio that were broken. I cut the bad area out of those and soldered/heat shrink and it works again too.

Too bad I didn't do pics but it's just wires....it would have been boring.

It does take time.

Dublinoh

The fix in my case was just to strip, twist and solder. Then some shrink wrap. I cut back a plastic sleeve that has like fifteen wires going through it. It seemed to make the wires bend right where they exited the sleeve and I wanted them to bend someplace new. It does take some time, but in my case only one wire needed repair.

Dublinoh

Well this is my third post on this thread. If you have an inoperable auto trunk function, and have had a Third brake bulb warning intermittently, license plat light left, etc. The wire loom follows the LEFT trunk hinge assembly and is prone to broken wires. These problems are probably not one of the computers, (rear bus?). Today I fixed my broken ground wire again, adding some length this time by splicing in about four inches of same gauge wire. Access is possible without removing panels, just free them up by removing six or so push fasteners and push or prop aside. My trunk was not closing all the way, and then stopped working at all. Now it closes as it should. Plastic conduit is where my brake occurred.

Yuille36

Sometimes, you can't detect a broken wire, when the plastic protective sheath is still intact. You have to check resistance at both ends of the wire.
As our cars age, so does the wiring. They tend to get brittle, and are prone to breaking if constant bending force is applied to them over and over.
But you all know this by now.

MJBelcher500

I just recently retrofitted the trunk closer on my E55. I purchased a new button harness from the dealer. It was only around $50. For those that would rather not repair this is a relatively inexpensive option.

Part number for harness (with KeylessGo) is 2115404810. I purchased mine from: https://www.mercedesbenz.parts/oem-p...s-211540481098