Security Update: Central Locking Defeat for 124, 126, 210 - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 07-28-2010, 01:09 PM

It has occurred to me that there might be times when a driver might need to unlock the driver's door without unlocking all of the others. Such situations might involve a "bad neighborhood" or a woman driver alone -- you get the idea. Here's what I am planning for my '87 300D Turbo (W124, OM603). This should apply to all 124s and to other MBs with an electric Central locking System (CLS), such as the 126 and the 201. Sorry, this method will not work on a 123. You would have to do some vacuum line plumbing.

You probably know that the mechanical key-cylinder locks in the driver, front passenger, and trunk/tailgate doors have an electrical switch. When the key (or the inside knob) is used to lock or unlock the door, the electrical switch operates the pump and locks or unlocks all of the other doors. To defeat the CLS, all you have to do is to disconnect the wire from the driver's door to the pump.

In the 124, this wire is blue and it attached to pin 2 of a round three-pin connector that plugs into the pump, which is under the right side of the passenger seat. In the 126, the pump is in the trunk. I don't know where the pump is in the 201. With the blue wire disconnected,
(a) The key (and the inside lock knob) will continue to lock and unlock the driver's door but will not operate the pump so none of the other locks will lock/unlock;
(b) The right front door and the trunk/tailgate will continue to lock/unlock all of the other doors through the central locking system as usual;
(c) If you have an aftermarket keyless remote system, as I do, it will continue to operate normally, locking and unlocking all of the doors.

If you need to restore normal functioning of the CLS on a regular basis, you could install a switch with "Normal" and "Defeat" positions. In "Normal," the blue wire from the driver's door to the pump is connected; in "Defeat," the wire is disconnected. This switch could be put in the dash, hidden under the seat, whatever you want. Having this switch is more important if you don't have a wireless remote system.

You can also get more sophisticated. For example, instead of breaking the blue wire from the driver's door to the pump, simply break the +12V wire (red w/white stripe) at the switch in the driver's door. (This requires removing the door panel or the left front kick panel to access the wire.) By breaking the hot wire, the key switch and inside knob will continue to lock all of the doors but will unlock only the driver's door. The reverse could also be done by breaking the ground (brown) wire. Then you could unlock all of the doors from the driver's door but you could lock only the driver's door. Why you would want to do this I cannot imagine.

Jeremy

LoosBenz · #2 07-28-2010, 03:54 PM

This is great! Thanks!
Just a couple of questions, though. I have no keyless entry and am considering adding it. I am spoiled on my wife's Subaru having a button that is pushed once to unlock the driver side door and twice to unlock all. I am considering using an aftermarket keyless system and wiring it so that it works in a similar manner. I'm assuming that a relay activated by a key fob could be used to apply 12V to the blue driver side wire or the wire operating on the passenger side. Does the pump module have its own timer incorporated so it stops after a given amount of time when activated by the lock switches?

Jeremy5848 · #3 07-28-2010, 04:41 PM

Quote:

Originally Posted by LoosBenz

This is great! Thanks!
Just a couple of questions, though. I have no keyless entry and am considering adding it. I am spoiled on my wife's Subaru having a button that is pushed once to unlock the driver side door and twice to unlock all. I am considering using an aftermarket keyless system and wiring it so that it works in a similar manner. I'm assuming that a relay activated by a key fob could be used to apply 12V to the blue driver side wire or the wire operating on the passenger side. Does the pump module have its own timer incorporated so it stops after a given amount of time when activated by the lock switches?

I looked into that -- my aftermarket keyless remote has a feature like that -- but the Mercedes Central Locking System (CLS) locks or unlocks all of the doors, trunk, and gas flap at once so I can't use the feature. The hoses run to all of the locks and they all operate together. Electric locks are a lot easier to modify.

My keyless remote uses two relays to operate the CLS remotely while still allowing the key locks and door buttons to lock and unlock all the doors.

You would need to install some electrically operated valves so that the driver's door could be isolated and unlocked separately. This is possible but I'm not sure how big a project it would turn out to be. In particular, the hoses are buried under the carpeting and might require you to remove the driver's seat to break into the hose that runs from the pump to the left rear door and then to the driver's door.

The CLS pump must have a timer built in because it runs for a few seconds and then shuts off.

Sorry that I am unable to put a more positive spin on your wish, it is a good idea.

Jeremy

LoosBenz · #4 07-28-2010, 07:02 PM

Oh no, you answered my question and if everything works as it would appear, I think it is quite doable. Thinking back, I probably only need to tap into the blue driver side wire to apply power as needed rather than tapping into the passenger side, as well. Most of the rest would be handled by solenoids to control air flow. I'm thinking tapping into the pump motor supply (if accessible) to power the solenoids (via relays) only when the pump is running taking advantage of the built-in timer. The next question would be how volume sensitive the system is. Is something going to blow up because only the driver side lock is being operated?

Jeremy5848 · #5 07-28-2010, 10:52 PM

I doubt that anything would blow up. Remember that the same pump also operates the optional "orthopedic" seat cushions (no, I've never seen them either) so it must be able to handle various volumes/pressures of air.

You can certainly tap into the pump's DC supply but to do so after the timer means opening up the pump assembly (I suspect that is possible) and tapping onto the motor leads so that your solenoids would operate only while the motor was running. You would also need to run a separate air line for the driver's door lock. If you're capable and willing to do that, it appears doable and I would be very interested to see what you come up with.

Make sure the solenoids don't draw a lot of current, I don't know how much the timer can supply. You might want to measure the motor current and keep the solenoids to no more than 10-20% of motor current. The schematic shows only a box with a transistor symbol in the middle for the timer and associated electronics and I've never disassembled one but do have a spare on the shelf.

Jeremy