1987 W124 vacuum lock question - PeachParts Mercedes-Benz Forum

Hupomone · #1 04-11-2016, 01:39 PM

My vacuum lock system was a compromised from the leak into the passenger side foot well. I got a new pump that I have verified works in both push and pull. When I connect it directly to the battery (the power to it has a short somewhere) and then use any of the door or trunk locks the pump kicks on and locks all the doors, trunk, and gas door. However when I unlock at any of the doors or truck nothing happens?

Any ideas?

Thanks,

Geoff

jay_bob · #2 04-11-2016, 02:25 PM

The pump works like this:
There are two connectors, a flat and round.

The flat connector gets constant power from fuse C. Pin 1 is ground (brown), pin 2 is switched ignition for the ortho seat version (empty if not), and pin 3 is power from Fuse C.

The round connector has 3 wires. These are the signals from the doors and trunk/hatch switches. Each wire works the same. Applying +12 V to any of these wires tells the pump to "unlock" and applying ground to the wire tells the pump to "lock".

Hupomone · #3 04-11-2016, 02:48 PM

OK, so mine will lock so the ground is good? but will not unlock so its not getting power? Since I have the power direct wired from the battery to the pump, I know that the pump is getting power. Is there a signal issue from the locks? It seems universal all will lock none will unlock? Since they will lock I am guessing that the wires are good since it is only one from each to the pump that sends both signals. Where is the problem?

jay_bob · #4 04-11-2016, 04:00 PM

The 12 V supply for the switches comes from the same place as the constant 12 V for the flat connector. So if you are having issues with the power feed then chances are the lock switches aren't getting their 12 V either.

Do you have a wiring diagram for the car? Go to Model 124 Maintenance Manual Index

There are inline splices in the wiring harness between the X30 distribution block (under the driver's side footwell kick panel) and the pump. Pwogaman had this problem:
1987 300TD W124 Wagon...DC Impound Auction...$450 Ends 07/18/2012

Or your wiring across the door hinge at one or more of the doors has flexed to the point of failure and shorted. Very common problem.

Hupomone · #5 04-12-2016, 04:02 PM

OK, I found the X48 connection, which is really just a a few wire nuts taped together. I cut them and rewired. I now have power to the pump via the flat connector! The trunk lock works for both lock and unlock. The drivers and passenger doors don't work for anything. I guess I need to pull the panels and evaluate the locks to see if they are getting power or if the wire is broken somewhere between X30 and the locks.

Thanks for the help.

G

Maxbumpo · #6 04-12-2016, 04:49 PM

This:

Quote:

Originally Posted by jay_bob

There are inline splices in the wiring harness between the X30 distribution block (under the driver's side footwell kick panel) and the pump. Pwogaman had this problem:
1987 300TD W124 Wagon...DC Impound Auction...$450 Ends 07/18/2012

Or your wiring across the door hinge at one or more of the doors has flexed to the point of failure and shorted. Very common problem.

The stupid crimp joints in the right rear passenger foot well get wet, corrode, and go bad. IIRC there are two, power and ground, you need to fix all of them.

Hupomone · #7 04-13-2016, 08:26 AM

Quote:

Originally Posted by Maxbumpo

This:

The stupid crimp joints in the right rear passenger foot well get wet, corrode, and go bad. IIRC there are two, power and ground, you need to fix all of them.

I saw three. one power with 5 wires, two ground-one with 2 wires and one with 3 wires. I fixed all of them. I still don't have working signals from the front doors.

Next step (unless someone else has a better plan) is to pull the door panels and check the power and ground at the switches and then check the switches themselves.

G

jay_bob · #8 04-13-2016, 09:20 AM

Check the wires passing through the flex boot at the doors too.

MB used wire with a few thick strands instead of many fine strands. It causes the wire to fatigue and break with repeated flexing.

In extreme cases multiple wires can break and then short together.

babymog · #9 04-13-2016, 12:44 PM

These switches get cruddy in some climates, ... near the ocean?

The plug for this switch is in the doorjamb, it is a large black plug that pulls out, the electrical connection will come with it.

To remove the lock assembly open the door, pull the rubber plug in the jamb adjacent the door lock, back out the set-screw. There is a procedure of turning the key and pulling the lock out at this point for repair.

jay_bob · #10 04-13-2016, 06:58 PM

That is procedure 72-240

http://w124-zone.com/downloads/MB%20CD/W124/w124CD2/Program/Chassis/72-240.pdf