An E28 wiring question.

I'm sending an alarm unit to my brother who lives some way away - and all he needs it for is to provide remote lock and unlock for his '87 520 which
doesn't have it.
I'd like to give him chapter and verse on the connections and set the alarm up correctly. But I don't have a wiring diagram for an E28 - but do for an E34.
My idea is to fit the unit in the boot. And connect to the boot key switch which operates the central locking. According to my E34 diagram the key switch grounds either of the control wires which are coloured green/black (lock) yellow/black unlock.
And take the power for the unit from the boot light feed.
Any gotchas I've missed?
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*A backward poet writes inverse.*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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The green/black and yellow/black are the wires from the central locking control unit to the trunk locking motor switch. I do think grounding them will activate the lock properly.

The fact that remote control locks are adding additional crap that can go wrong, and the idea is silly anyway. Just put the key in the lock and turn it, all right? It's not hard. Sheesh. --scott
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Thanks.
;-) Do you have a lever on the steering column to advance/retard the ignition too?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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I'm not sure that you want to ground those wires. My guess is that they reverse polarity to make the lock go in the opposite direction. The locks have a switch on them that tell the central locking system to lock or unlock -- two switches, actually. But the wires leading to the lock solenoid are going to be the power that tells the solenoid to push or pull the plunger, they are going to be +12 and GND or GND and +12, depending on which way the solenoid is supposed to go. Since the solenoid is DC, then reversing the polarity will change the direction of the plunger. The wires going to the lock switches might be grounded to tell the locking system what the key is doing.
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Having said all of that, does the locking thingy act like the key OR does it actually power the lock solenoid(s), and if so, does it have enough power to operate all of them?
If you splice this device into the system, then press a button to activate it, whatever the device does to the lock solenoids, it will also do to the existing Central Locking System, and any activation of the Central Locking System is going to send the same signal to the newly installed device.
I don't know much but I know this stuff works by magic smoke, and I have the uncomfortable feeling that you're about to let the magic smoke escape. If you do it right, the smoke will escape from the Central Locking System and the newly installed device all at the same time ...
This should be a sight, do you intend to sell tickets?
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It can do it any way you like. The relays are 20 amp so capable of driving the motors directly. But my intention is to use the switch circuits.

Hence using the switch circuits. When you turn the key you ground one of the switch circuits. One for lock, one for unlock, depending on which way you turn the key. This device sends a negative pulse to either of the switch lines - so effectively duplicating the action of the switch.

I'd say you're right there. ;-)

Perhaps you need to learn how to read a wiring diagram. That's what my question was about - as I don't have one for an E28. Luckily Mr Dorsey has and understood the question. ;-)

That's what fuses are for. ;-)

If I were anywhere near the car I'd not be asking as I'd have worked things out myself. However, it's over 500 miles away and I want to give my brother simple instructions on how to do it.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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For a start they're not solenoids but motors - if the same as my E34. Dunno any central locking system that uses solenoids. They're not as efficient as a motor. On the E34, the boot switch does send a ground signal to either of the control wires for as long as the key is held in that position. And a control unit converts this into the pulse needed to operate the system.
The alarm unit (same as most aftermarket ones) has two changeover relays operated by the remote which can be configured any way you want - and also pulse for a time again set by the alarm. They can be used to operate the motors directly in other systems since they are 20 amp relays. But in this case it makes more sense to pulse the control circuits, since they are easily accessible.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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London SW

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Might just help others reading this to know what they're dealing with.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Yes - that's all it's for. And it came off my 'other' 25 year old car. To which I've fitted a more sophisticated one. ;-)

True - but older cars are often targeted by joyriders etc since they have little or no security. This alarm does have an immobiliser circuit if needed. And although it may have little value having a car stolen is inconvenient to say the least.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Don't forget, Dave, the ignition bypass that gets activated by locking the doors. You want to be sure that the device you are installing will enable the Ignition Bypass.
I wish I could help you more, but I'm struggling with a Trunk Lock Switch that won't unlock the doors, but will lock them. I discovered that if I turn the car OFF and climb out with opening the doors, then the trunk lock will lock the doors, but the Ignition Bypass is disabled -- somebody could get into the car and it will start.
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As I said all it will do is replicate the action of manually operating the boot lock. Nothing more, nothing less. So will have no effect on anything else.

The central locking has some form of controller - as obviously holding a key in the locked position would continually apply power to the motors. So in its most basic form consists of a timer which cuts off the signal from the switch after about 1 second. But it can also provide other functions like setting and disabling any immobiliser, etc. My guess would be that - or the connectors to it - is the problem. If you have a wiring diagram for the car it should be possible to trace what it's hooked up to as well as just the locking. However, my E39 has a very different boot lock mechanism to the E28. The central locking motor is spring loaded so returns to a rest position after operating. This is to allow the boot to be actually opened by the press of a button rather than just unlocked. There is a 'prove' microswitch inside the motor to tell things it has returned to rest. But I dunno the full logic of what does what on this system.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

I had some trouble with the driver door lock a few years ago. This car and the one it replaced would not unlock the doors from the trunk, but both of them have always locked the doors without any complaints. Anyhow, I removed the lock from this car -- '94 325 convertible -- and recovered whatever functionality I was looking to recover, and when I put it back in, I think I got something wrong with the linkage. To fix it, I have to open the door again and I've not bee excited at the idea of doing that.
What happens now is that the push-button on the door locks, and pops up when the inside lever is pulled, and it pops up when the passenger door lock is turned to unlock the doors, but it does not pop up when the driver lock is turned. I can come up to the locked car and use the key in the driver door, and the doors all unlock properly, except that the driver button does not come up.
I suspect I might have a problem with the proper alignment of the mechanism that is causing a switch to be set when it ought to be free. Having said that, I have to wonder why the passenger lock would unlock the trunk and driver door, the driver door unlocks the trunk and passenger door, but the trunk lock does not unlock anything but the trunk.
If I operate the ignition from ON to OFF, then remove the key -- or use a different key -- but do not open and close the door, then the driver door button goes up and down from any of the lock locations, but the ignition bypass featurte is defeated -- the car can be started while the doors are locked. If I operate the passenger door lock with the key, the driver door button goes up and down properly. This is all so confusing ...
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If it's like the E34 diagram I have, the control circuits from the three key switches aren't in parallel as you might expect. The door ones are - but the boot one is separately connected to the controller.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

I installed remote locking on my '92 535 yesterday. Following the advise in this thread I mounted the box in the trunk and connected it to the trunk lock switch wires. However, grounding the control wires only accomplished blowing a fuse. It turned out it needs positive voltage, which is also confirmed looking at the wire diagram, to operate.
The downside with the trunk location is that you can't close the windows and sun roof with the fob, and the "lock block" function doesn't work either.
Either way, I'm happy. Saves me the hassle of locking the doors manually anyways... :-)

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Interesting. My wiring diagram (Haynes) doesn't show the presence of a positive feed to the motor/switch - only a ground. But I'll pass that on to my brother.

No such modern nonsense on his E28. ;-)

He's replaced broken locks with secondhand ones so has too many keys.

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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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