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Old 02-11-2006, 02:45 PM
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keyless install issue... W124

Hey everyone,

searched the archives - not yet found the issue.

I need to know where to find a schematic for the wire harness at the vacuum lock pump.

Here is the rest of the story - if you are bored...

For starters - the tech help info I found was all slightly different than my model.

I have a 91 300e and the round harness at the vacuum pump has 4 wires - green / blue and two yellow.

I have a 3 second delay keyless unit from JC Whitney that will shut the locks down - and just after they are all down, they pop back up. If I grond the correct terminal my self (instead of the keyless) for a split second longer - they stay down. up function works correctly.

It appears that after the 3 second ground signal from the keyless - the system defaults to "open" status when the ground is removed - maybe a default so if you loose signal to the pump, the locks pop open for safety??

Does anyone know the color coding of my harness from the '91. It appears that I am tapped into the correct wire - as I am getting results - but need to find a way to control the ground (for the down lock function) better.

By the way I checked online and the crutchfield REC-11 unit is also a 3 second delay, so I know I have a long enough pulse.

Also, I do have one slightly slower lock (pass rear) - thought maybe there is a sensor on each lock showing up or down status causing part of the issue.

Thanks in advance,


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Old 02-11-2006, 11:26 PM
skiier3_9's Avatar
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Join Date: Jan 2005
Location: Minnesota
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I thought that you needed a 4 sec. ground pulse. I could be wrong though. Also, the locks will pop back up if a door is open i believe.
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Old 02-12-2006, 04:15 AM
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Location: Sherman Oaks, CA
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which wire did you cut into?

The way you are supposed to interface the vaccum locks is by cutting one wire and interfacing it with the keyless entry.

Here is how I do it, using relays to be trigger by the keyless entry.

I also tap into the blue or green wire, but not at the pump, in the passenger wire channel.

Vacuum Type Door Locks
Found mostly on Mercedes Benz vehicles, the movement of the door lock actuators is controlled by a central vacuum pump. The switch changes polarity on a single wire that may rest at power or ground depending on the state of the door locks. You can duplicate this with at least a 2 second pulse. If the alarm or keyless entry you are installing does not have a 2 second or longer duration option for the door lock outputs, do not use this diagram (it will not work unless you incorporate a timer into this circuit).

I always use bosch relays

Check out for some other great info on wiring things

My aftermarket alarm system allows for a 3 second pulse, or standard pulse, I am not sure if I ever set it to 3 second pulse, and never had an issue with my car locking or unlocking.

I believe there is also a convienience control module under the rear seat on the drivers side of your car you can also work with to interface the keyless entry. this link from our Wika may help you a bit.

Feel free to post in with more information.

I have found using relays combined with the aftermarket keyless entry system works best to provide good quality ground or power pulses required for door locks.
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Last edited by Ashman; 02-12-2006 at 04:24 AM.
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Old 02-12-2006, 11:54 AM
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Thanks !

I will do some more work and post my results...
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Old 02-12-2006, 04:18 PM
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Join Date: Feb 2006
Posts: 10
ashman - check your email...

I have a question and sent an email regarding the up (or 12v pos) trigger from the keyless unit...

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Old 02-13-2006, 08:49 AM
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Join Date: Dec 2002
Location: New Castle County, DE
Posts: 1,032
I had to set my JCW unit to a longer duration pulse to make it work. Also had to run a disarm wire to the alarm unit (It armed fine all by itself).

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