I am trying to get my central locking system working (which did not work when I bought the car). My old pump was inoperative and had some corrosion on the circuit board. I tested the power harness to the pump and I am getting 12v. I tested the pulse from the door actuators and I get some voltage, but not spec.

I bought a new pump (124-800-21-48) from MB and installed it. I also bought a keyless entry system (REC-11 with DSLV) figuring that I could bypass the possibly faulty door lock actuators.

My doors unlock and lock properly with vacuum/pressure applied at the vacuum line attached to the pump and the system holds vacuum, by the way.

So, I install the new pump (first without the REC-11) and it does not turn on. I figure it needs the pulse from the door actuators to turn on. However, I tried applying 12v to each of the three "signal" pins on the pump housing and I get nothing. I try ground to the signal pins and nothing. I install the REC-11 and it seems to work and I get a pulse signal (changed to 3 secs as required) but again the pump does not turn on.

Does this sound like a bad pump? Am I correct in assuming that I should be able to get the pump to run by applying 12v to one of the signal pins? Anyone know of any other way to "bench" test the system, or should I just get the pump replaced? Thanks.

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1987 300TD 231,000
#22, afterglow, plastic fan, euro lights, alternator upgrade, cluster housing update

The problem was in the terminal connections in the raceway. The connections were just good enough to register 12v at the pump wiring harness but not enough to drive the pump. I bench tested the pump at the fusebox with three alligator clip lines. Wire up the pump to ground and the top of a fuseholder and then attach a clip to any one of the three pins at the round connector. Ground the other end of the line and the pump should run. Next energize the line at one of the fuse holders and the pump should run.

I resoldered the three connections in the raceway (two of the three were bad) and everything, including the REC-11 keyless entry, works as it should. I have attached a picture of the raceway and the wiring within.

Use caution as the wires may be quite brittle. One of my red wires to the front doors snapped and I had to splice in a replacement section. The wire was very corroded where it snapped, which was a good 6 inches from the terminal connection.

Attached Thumbnails

 

__________________
=-=-=-=-=
1987 300TD 231,000
#22, afterglow, plastic fan, euro lights, alternator upgrade, cluster housing update