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Old 08-23-2004, 07:39 AM
Coming back from burnout
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
Is anyone running a electric vacuum pump vice using the engine driven version?

Has anyone replaced their engine driven vacuum pump with an electric model. This applies to my 1987 Mercedes 300D where I cannot get any vacuum to operate the Central Locking system because I cant get the onboard electric version to work(The pump runs, but will not function because it gets no signal from the door actuators)
I am thinking of installing my own electric vacuum pump or connecting to the Engine Vacuum.
Can anyone recommend an electric vacuum pump model and comment on its lifespan?

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Old 08-23-2004, 01:51 PM
Registered User
Join Date: Jan 2002
Location: Colorado Springs, CO
Posts: 1,006
How did you test the electric pump under the rear seat?

If it has in fact failed, I have a used one available.

Brian Toscano
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Old 08-23-2004, 02:21 PM
Coming back from burnout
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
I stuck a jumper from the 12 V wire

that is always hot to the one that is hot only when the engine is in start position and the pump came to life. It did so only briefly. I can repeat this agian and again by returning the ignition key to start.
The pump has two connectors; one has a Black, Brown and some other color wire and the other connector has BLUE, GREEN and YELLOW wires and these wires are connected to the A, B and C points which are the three main locking points on the car. I am not getting the 10+ Volt signal at any of the A. B, or C points which come from the three main locking points on the car like the diagnostic sequence says I should by locking/unlocking at these points.
Once after driving through a heavy rainstorm, the central locking system came to life for quite a while. It stopped working during my recent overhaul and this may because I disconnected the car's alarm system which is tied into the cnetral locking sytem at the A, B, C connector.
I was going to run a line from the engine vacuum pump but I dont know if teh car has a vacuum reservoir.
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Old 08-23-2004, 02:25 PM
Coming back from burnout
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
its nice to have the CLS

rather than locking the doors individually. Obviously its not as important as things like basic mechanical integrity of the car and I may be overdoing it, but I like to try and get everything running...
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Old 08-23-2004, 05:17 PM
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Join Date: Jan 2001
Location: California
Posts: 2,068
The engine's vacuum pump has NO connection to the locking system on the W124. The electric vacuum pump and the vacuum lines for the door locks are isolated from the engine. The problem is either with the pump or the wires in the lock cylinder. First of all, do the locks operate when using the key in the passenger's door or in the trunk? If not, the culprit is most likely the pump. As you mentioned, there are two harnesses on the pump. One is red and brown, and another is blue/green/yellow. The red wire should have 12V constantly (always hot), and the blue/green/yellow wires receive 12V or ground depending on which front door or the trunk is (un)locked. While 12V is applied to the red wire, apply 12V to either of the pins corresponding to the blue/green/yellow harness. The pump should run as long as the wire is touched to it. While the pump is running, put your finger over the vacuum connector. It should stop. Now for the pump to run again, apply ground to one of those terminals. It should run.
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Old 08-24-2004, 01:41 AM
Coming back from burnout
Join Date: Jun 1999
Location: in the Pacific Northwest
Posts: 2,274
Thanks a lot, Speedy!

Thanks a lot...for a second I thought I was the only one out there wasting his Saturday afternoon fixing this.......

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