central locking system electrical problem

[1987300sdl]

My central locking system quit working on my 87 300D.
I have searched through many posts, including a very helpful one by Kenhartz back in 2011, but still cant pinpoint the problem.

I have check my x30 box, and dont see any sign of corrosion or any other problem.
Checked fuses-they are fine.

I have verified that the system holds vacuum very well for long period of time.
Following instructions by Jeremy in:
HELP!! 87 300D central lock nightmare! I cant get the doors to lock or unlock at the pump.

I have put 4 different pump from old cars in my car as a test, but I still cant get my central locking system to work. (The locks function manually just fine)

I traced the 3 wires from connector 2(at the pump) to the brainbox for the security alarm. they ohm out just fine.
My security alarm works fine. (I even replaced the brainbox under the passenger footbboard-as a test.)

Can anyone offer any assistance here??

I find it hard to believe that all 5 of the pumps are bad, but it is possible. Can anyone tell me how to bench test the pump??

Thanks for your assistance.

[ah-kay]

It is easy to test the central lock pump, in the car or on the bench.

1) Connect 12v to pump with the rectangular connector.
2) Remove the round plug.
3) Disconnect the vacuum line leave it open.
4) Use a wire, ground one end to chassis and touch the pins where the round plug is inserted. Any pins will do. It will activate the pump to suck ( to lock the door, so to speak ). There is no vacuum line so it will keep sucking for approx 30 sec and times out. The pump is in lock state.
5) Use a wire, connect one end to 12v and touch the pins, any of the 3, and the pump will push air ( to unlock, so to speak ). It will time out also as there is no vacuum line. Pump is now in unlock state.
6) Redo step (4) and (5) but with the vacuum line plugged. You should find the pump stops immediately as it thinks the door is fully lock or fully unlocked.

Hope this help.

[1987300sdl]

I have more problems than I thought.

I dont even have 12V at the red wire.(I did the last time I checked)
The fuses A and C are good. I checked them with an ohm meter.

Does anyone know where it comes from/how to trace that backwards??

Also,I have 5 pumps that I have accumulated over the months trying to fix this problem. Since I dont have 12v, I have to use a Jump Box to test on the bench. Four of them dont respond at all.
On one of them, I went through steps 4 and 5 the first time. It was looking good at first. A friend of mine put his thumb over vacuum port, to see if it was pulling vacuum, and the motor shut off. Now I cant get in to respond at all.

Does anyone know if a pump from an 87 300SDL will interchange with an 87 300d?? I can get one at a good price.

[lorainfurniture]

Under the carpet at the front foot well. Right where your right foot goes. There is a connection that supplies the power to the red wire. You have to undo the wrapping and everything. Once you find a clear tube thingy that is all green and corroded you found your problem. Cut, strip, wire nut, and you are good for another 20 years

[1987300sdl]

Are you talking about the x30 block? (under the brake pedal)
I have already checked that, it there is no corrosion/rust or anything else.
It looks normal.

[lorainfurniture]

No. PASSENGER side. It literally is a bunch of power wires that are joined within the wire harness. It's hard to explain.

Pull the carpet, then pull the black plastic cover. (Please bear with me bc I did this 2 years ago). You will find a bunch of wires that go to your vacuum pump. Somewhere near the base of the wheel well you will find the corroded connection.

You really got to dig for it. If you start, snap a picture and I can direct you a bit closer.

[ah-kay]

Originally Posted by 1987300sdl

On one of them, I went through steps 4 and 5 the first time. It was looking good at first. A friend of mine put his thumb over vacuum port, to see if it was pulling vacuum, and the motor shut off. Now I cant get in to respond at all.

Does anyone know if a pump from an 87 300SDL will interchange with an 87 300d?? I can get one at a good price.

Pull the power and see whether it works again. The pump remembers what state it is in. If you ground it to lock, it will not response if you ground it again. It needs to be in sequence. Are you sure all 4 are kaput? They are quite reliable. I have never opened one up, there may be a fuse inside.

I think the vacuum pump on all MBZ are pretty much the same. I have used VP pulled from Gas cars. 300SDL VP should fit 87 300D.

[1987300sdl]

LorainFurniture-
I have taken a picture with the footboard removed, and a picture with the kickpanel removed.
If you see a red wire and a white wire, they were there when I bought the car, and they are not connected to anything.

[1987300sdl]

ah-kay,
I thought about something like that. I did my test yesterday, and again today. I would certainly think that would be enough time. I have taken some apart. There aint not fuse.
Just a motor, and circuit board, and another device.

[lorainfurniture]

Originally Posted by 1987300sdl

LorainFurniture-
I have taken a picture with the footboard removed, and a picture with the kickpanel removed.
If you see a red wire and a white wire, they were there when I bought the car, and they are not connected to anything.

Email them to me at lorainfurniture at yahoo . Com. I can't see them on my phone.

[1987300sdl]

I emailed them a few minutes ago

[lorainfurniture]

Replied

[1987300sdl]

Eugene,
The central locking system is working now!!! I got a wiring diagram and figured out that you were talking about he x48f connection. I searched this forum for x48f, and found several pages that I hadnt seen before.
As others indicated, the red/white wire looks good on the outside. and since it is all protected from outside elements, one wouldnt expect corrosion. But, when I cut it, you could see the green inside the wire. I spliced another wire into it, and got my 12 volts, and then got a good pump, and whallah!!

For those searching for answer in the future, search for x48f, and you will get many hits, and much helpful info.
Thanks again!

Now, all I have to do is figure out why I cant get my passenger front seat back far enough for someone to get in!! that is my next project.

[1987300sdl]

ah-kay,
I found that I had 3 out of 5 bad pumps, including my original pump!
Thanks for the the help!!!

[lorainfurniture]

I wish I knew what the connection was called, I had to do it the old fashion way. Good job on finding the issue.