Central Locking Gone Again

[MGTF_avengers]

Well, I found out what happened.
The door actuator was replaced again.
The previous replacements were from a faulty batch.
This new one is working OK still, so hopefully its all been sorted now.

[Rob Bell]

It takes time to investigate, and if the latches are known to be faulty, it may be quicker and easier for them just to replace and not think about it too hard.

Repeated replacement worked in Martin's case, so fingers crossed here too.

[Ian]

I have also been having a few problems with my alarm going off. All seemed fine until I "enthusiastically" shut the driver's door whilst pushing the locking down at the same time ( the system spits up the pin again to stop you locking yourself out !). Long story short, I discovered that one of the micro switches had failed in the driver's door lock. I managed to get a replacement lock from ebay (£25) which had certainly seen more life than the one I originally had. However, now replaced and was working fine until the damn alarm going off again !. This set me off on my mission to find out how the locks actually work,what the micro switches do and how it can fail.
So here goes: I have attached photos of the internals of the drivers side lock.

3 micro switches. Bottom one is lock SENSE, open or shut. Middle switch is DOOR open or shut, top switch is KEY sense turned in the lock.

door lock drivers side.png (132.8 KiB) Viewed 470 times

Once you have it removed from the door you can carefully take out the screws which hold the top plate on. I would suggest that you don't tip up the lock while you do this, if you are unfamiliar with the internals some of the components will cascade on the floor and you might be scratching you head on how it went together !. With the motor pointing upwards, once all screw removed, carefully take off the top plate. You will find that there are 3 micro switches at the one end of the lock. These are for:
1. lowest one in the photo - is the lock closed / open sense - two wires, Grey and Red wires used to determine the lock closed or open with a ground to the appropriate state (see my hand drawn diagram attached)
2. middle mounted micro switch - this works with the long white(ish) lever you can see in the photo. It tells the alarm that the door is CLOSED - again see me hand drawn diagram. This switch wasn't working in my replacement lock due to wear on the operating lever. So I glued a very thin bit of plastic to lengthen the white lever by about the thickness of flexible card. This solved the problem for me. In the passengers side door lock, this this is ONLY micro switch which is present - the alarm only needs to know if the door is open or shut on that side.
3. Last micro switch you can see operates with the KEY being turned in the door lock. Again see my hand drawn diagram, it basically earths the white wire to the alarm which I guess fires the locks open or shut depending on the last state it went to.

circuit diagram of the 3 microswitches and colour of wires to them.

I am currently refurbishing my previous lock where the bottom microswitch failed (the one that tells the alarm that the door had locked). I have no output on the grey wire. I have managed to source replacement micro switches from Maplin Electronics ! - part number: N96AQ Min Microswitch. The dimensions are the same as the originals however they will require some fine tuning when fitting them - 3 need to be ganged together and secured at just the right place to work on all three actuators in the lock. I hope this helps anyone else figuring out how it all works !.

UPDATE!: Now used Maplin Microswitches N96AQ which have adjustable levers. See my final fixed lock photo included in this post.

3 maplin switches in place. The metal levers need small adjustments to make sure the lock actuators work the switches !.

The upper most micro switch lever will need about 2 mms taken off the end of the lever to stop it touching the large black gear wheel. The metal levers on the switches are adjustable, so you will need patience and time to adjust them by bending here and there to ensure they operate correctly. I used 2.5 mm machine screws, 25mm length through all 3 switches to fasten them into existing holes in the casing. Two 4mm holes will need to be drilled carefully within the top motor plate to accommodate the screw heads ( the plate sits over the heads). I wired the switches so that all the "common poles" are connected to the black wire (transposes to the earth connection when fitted to the MGF). Apply a few touches of grease here and there to ensure all runs smoothly. So it is possible to repair your lock if the switches fail - it does take plenty of time and patience though ! - total cost of repair: £6.27

Let me know if you want anymore photos etc.

Cheers. Ian

[MartinW]

Brilliant information, thanks, this will be very useful. Was your lock rattling, too?

[Ian]

Hi Martin, the locks were operating without any strange noises, but with one microswitch broken the alarm couldn't work out it if the locks were closed or not !. The "clickety, clickety,clickety" noise that many owners mention must be to do with the motor assistance in the lock continually rotating because the Lucas alarm hasn't received the "locked " status and also "door shut" status. Several reasons for this, main ones being the microswitches not working correctly, or some mechanical failure due to a breakage in one of the internal parts ( which leads to the micro switches not working !).If the owner has time, I would recommend taking out the door locks and greasing or oiling the plastic component system. It will take a lot of strain from the mechanism and hopefully nothing should fail due to lack of lubrication.
I'll post photos of my "refurbished lock" with the new Maplin switches when I've done it. I notice that the original micro switches were more lock friendly in that the actuators didn't need to be too smooth edged to work. A tiny bit of smoothing where required with a mini file will sort that and some grease .

[Rob Bell]

Really nice work Ian!

It will be interesting to see what the commonest cause of microswitch failure is - mechanical actuation or a problem with the microswitch itself.

Which microswitch from Maplin are you planning to use Ian?

[Ian]

Pic 4.pdf

Lock Pic 4 of 4

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Pic 3.pdf

Lock Pic 3 of 4

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Pic 2.pdf

Lock Pic 2 of 4

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Pic 1.pdf

Lock Pic 1 of 4

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Hi Rob.

Hopefully 4 .pdf documents attached of the assembly

Maplin Switches are: N96AQ

[Rob Bell]

Thanks Ian - really useful pictures. Looking forward to seeing how you replace the lower microswitch