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#1
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83 300sd central locking system electrical problems
Alright...Ive taken the information from the following two very good posts and went to work on my defunct central locking system:
83 300SD Door Locking Vacumn Pump Problem Door locks 1982 300SD W126 Here are the things I know and have found through troubleshooting: 1. The pump in the trunk works. I rebuilt one out of various ones pulled from the junkyard and when it is hooked up to a battery charger (or a battery) both the vaccuum action (locking) and the air pumping action (unlocking) works perfectly. 2. The red and black wire going to the drivers side vaccuum element (referred to in other posts as a pod) has 12.8 volts running to it. This would mean the fuse is good too. 3.There is continuity on both the yellow (unlocking) and blue (locking) wires between the drivers door vaccuum element and the trunk. 4. When I hook up the blue wire and the red & black wire at the drivers door I get 12.8 volts on the blue wire in the truck. The same can be said about the yellow wire. So there is not only just continuity but plenty of juice. 5. The Ground (brown wire) in the trunk is good. The following are my problems: 1.With the pump hooked up...when I touch the red & black wire with either the blue or yellow wire the pump does not activate. Despite this I can still read 12.8 volts in the trunk where the connection is exposed. How is this possible when the pump bench tests perfectly????? 2.The connecting piece that attaches the three wires (red & Black, yellow & Blue) to the vaccuum element in the drivers door has completley fallen apart. It seems every connection Ive seen like this has disentegrated. Has anyone experienced the same thing? I reinforced the one for the pump in the trunk with epoxy so it wont fall apart as well . My question is which prong on the vaccuum element corresponds to which wire? Any help at all would be extremely welcome because I really don't know where to go from here.
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1983 300SD White with Grey interior |
#2
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It sounds as if you have a leak in the system and it is not causing the Sequence Pressure Switch to toggle between lock and unlock. This switch has to make in order to switch power/direction of the motor. This switch is connected to the blue and yellow wires, on one side, and the motor for the pump on the other. A diaphragm actuator drives it back and forth. When you bench tested, did you connect to the pump itself or use the blue & yellow input wires?
Also, I haven't had to deal with any problems in the door switch so haven't seen the disentegrating problem. According to the diagram, connections for that switch are yellow=switch #2 and blue= switch #3.
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Sam 84 300SD 350K+ miles ( Blue Belle ) |
#3
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Well I got it working (thank god) after hooking up the battery charger to the lines going from the door to the trunk. I guess the higher amperage might have rejuvenated the lines a bit after they hadnt been used for a long time. That and a wire brush on the lead from the fuse (red & black) got it all working again. Connections are everything I guess.
As far as connecting it to the vaccuum element I got that figured out as well. I still wish MB made that little plastic piece that holds the three wire prongs/ends a little more durable. I'll probably make something of my own out of epoxy so the connection doesnt come loose. I do have vaccuum leaks and I guess thats my next project to tackle now that the electrical side is done and working. I have a feeling its the passenger side actuator.
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1983 300SD White with Grey interior |
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