Fix Boot Lid Lock Random Opening Problem

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Hi all,

looks like after 10 years this thread is still very much alive. I guess that as long as these cars are around this will be the case.... here is my take on this....

My problem started yesterday on a 2005 Focus 1.6 Petrol.

It looked initially as others say that the boot lock opens at random times.... well in my case it looked that way until I found a repeatable action that I can replicate every time... so in my case it's not random.

It happens when I depress and release the brake pedal.

Here is what I tried so far.

Facts I:

- Locking mechanism unlocks every time I release the brake pedal

- The Micro-Switch on the boot does not work, it does not unlock the boot as it used to 2 days ago

- Remote (plip) boot unlock still works

I removed the boot lid plastic cover and undid the 4 x 10 mill nuts to loosen the black plastic trim where the micro-switch is housed. Of course when removing the rubber cover from the body it was all wet and full of lime scale. However, when pushing the swivel plate off the way to uncover the micro-switch button, this one actually looked clean. I removed the connector and pulled the whole switch assy of the trim.

Facts II:

- the micro-switch works flawlessly. With a multimeter I could confirm that this is not the faulty part, even though there is the question why it doesn't give the lock the opening signal.

This now seemed a bigger problem. Even with the switch removed from the vehicle and using the brake pedal I could here the locking mechanism working. So I have a much bigger problem than just the switch.

Next thing was to remove the locking mechanism and check it out.... at this point my mind was wondering already about the problem being somewhere else and not the lock, but I continued.

Removed the lock just to reveal that it looked dry and clean. Detached the electrics to the lock and here is where I could support the idea that I had a much bigger problem.

The white plastic connector has 6 points/pins

so you can have an idea how I looked at it; the two empty points are on the left.

from left to right now

Points 1 and 2 - empty (no connections)

point 3 - battery (that's all I could think of as voltage is around 12V

point 4 - with and without ignition ON 10.60 to 10.75, respectively 

point 5 - Ground?

point 6 - Ignition OFF at 0.28V; ignition ON 5.88V. I can only assume this is the signal point. When I open the boot via the remote this point changes voltage, but it's so quick that my multimeter cannot display the value and drops back to 5.88V. And as expected when releasing the brake pedal the same signal appears.

Here is where I cannot continue as I don't have the electrical schematics for this car. I thought that it could be related to the stop lights so I checked all 3, by cleaning the mess under the light housings to reveal clean and sealed cables.... so also nothing here. The 3rd stop light looked very wet when removed, but also here I couldn't see anything wrong.

The question is now where does the signal cable go and where would it be interacting with the brake lights signal? Also, why does the micro switch not work.... I forgot to check if there was any feed to the switch, my bad....


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Check all the wires that go through that flexible shroud for cracked/rubbed covering over the wires especially in the bent bit, that,s where we found exposed wires on my Focus that was giving the 'Boot Open' message.

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I concur with that.
The boot is unlocking due to a short between thw brake light loom and the lock solenoid loom.
Older cars get this problem usually due to perished / brittle cable insulation which snaps and allows moisture to bridge the wires and cause the short.
Check the roof loom where it goes to the hatch, I'm 99.9% sure you'll find cracked insulation and moisture present.
All you need to do is cut out each wire 2-3 inches either side of the break and solder or crimp in patch cables (of matching guage wire) and seal with shrink tubing to keep the wiring joints dry and protected.
The hardest bit is getting access to enough wire length to cut back behind the headliner without bending creases into the liner itself.

Sent from my SM-G930F using Tapatalk

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just went out to test your theory and it worked.

I loosened the cable flex conduit on both sides exposing the black wires. As a comment: there are only black wires and these all look having the same core size which will be a pain to know what is what there, but I suppose I only need to find the culprit ones.

whilst wiggling the wires that go into the roof nothing happened..... but as soon as I started to wiggle the ones that go into the lid the locking mechanism started clicking as if someone was forcing it to open, which was great to see or hear as it must be where the problem lies.

So well done guys in pointing me to this part of the car.

So now the next step will be finding where exactly the wires have become exposed. If I remove the hatch spoiler will I have better access to that area where the cables come into the lid? Because if this isn't the case I don't see how I would be able to do anything without having to strip the whole harness out. Any ideas guys?


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I think I can answer my own question...... but please confirm.... I will have access to the harness by removing the trim on top of the gate, so it's not the spoiler on the outside but the trim on the other side (interior) this should allow the access right?

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