My car has a few electrical gremlins which I'm interested in hunting down and I was hoping to get some insight from those in the know. There are a few separate issues, all of which I'll mention because they may or may not be related to one another.

#1) Central Locking Inop:

I pulled the rear seat and found the pump. The PO had apparently monkeyed around with the wiring at some point because I found a new (fused) lead coming direct from the battery to the 2 prong connector on the pump, and it appears someone had added a new 3 prong connector to the existing harness using butt connectors. Connections all seem good.

The power plug for the pump has both power and ground.

When I disconnect the 3 prong connector from the pump and apply 12v power to each of the individual pins on the pump itself, the pump will power on and the door locks function as expected. Conversely, if I apply ground to the pins on the pump it will power on and the door locks all work as expected. (At the moment I can't recall whether applying power locked the doors and ground unlocked them, or vice versa, but either way all doors locked and unlocked when manually sending 12v or ground to 2 of the 3 pins on the pumps connector.)

I plugged the 3 pin connector back into the pump and unplugged the other 3 pin connector nearby. This other connector had one side with 3 colored wires, and the other end of the connector had a white wire leading under the passenger seat. Applying power or ground to the white side of this connector netted the same results as applying power/ground to the pump itself. The doors lock and unlock.

After fiddling around with all of this stuff, I just happened to manually lock the trunk with the key and was able to hear the pump kick on for a second. Unlocking/relocking the trunk (or anything else) did not net any further results.

So as far as diagnosing my central locking issue, where should I look next?

#2) Rear windows inop

Fuses are good. Pulled the front console and swapped all of the switches around. Switches are fine since they operate the front windows without issue. No noises coming from the rear doors that I can hear when operating the switches. Used a test light on the rear window connectors in the front console and found power on one pin in each connector. Pulled one of the the rear door panels and used my test light on the switch connector and could not find power on any of the pins. Inspected visible wiring in door, looks good as new. Pulled cover from pillar and inspected visible wiring, all looks intact, although I did find a disconnected power lead near the rear door switch which doesn't seem to have anything to connect it to.

Where do I look next?

#3) Rear door switches/lighting inop

Opening and closing the rear door does not toggle any of the interior lights. When the front doors are open, the lights in the rear doors do not light up, however when manually turning them on via the switch in the dash they do light up. Used test light on rear door switch connectors and found no power at any time.

#4) Rear power headrests inop

Haven't even begun to troubleshoot these, not really a huge deal, but it would be nice if they worked. Where do I even begin?

#5)OEM Becker Radio Inop

The radio powers on but no audio can be heard from speakers. Also, when using the "automatic" tuner button it never locks onto any channels. Any likely causes I should look into?

I'm not expecting miracles here, but any insight would be helpful.

If the pump works, then the trigger for the pump is obviously broken. I would verify continuity and power at the pump (sounds like you already did that), and trace it back to either the drivers' side or passengers' side door lock switch inside the door shell itself. The other option is to get a mityvac and make sure all of the vacuum connections are sealed properly (though you said you locked the doors by accident? that would indicate it was all hooked up). I would lean toward the lock triggers in the door (they're not officially called that, can't think of the name off the top of my head)

I had trouble following this. Sounds like you are not getting power at the switches in the console? Again I would backtrace the circuit and look for any wiring faults.

These are vacuum operated through a solenoid and are quite a complex system. I would wait to tackle these until you have the vacuum pump working again, might kill 2 birds with one stone.

Pop the fader out and see if any of the wires are disconnected, if not, play with the fader a bit. That is a common failure point as it gets old and people spill all sorts of stuff on the center console over the years due to no cupholders. From there on its tough to tell - the w124s came with a variety of audio systems. For starters - does yours have an active bass system (speakers in the doors)? That gets a separate amp in the trunk to power the speakers. Also, the tuner has a separate module IIRC, so the whole system is broken down into various components. By far the easiest way to get everything working again is to install an aftermarket head unit and run new wires to all the speakers, bypassing the fader. However, I do realize that solution compromises the originality of the car and is not necessarily embraced by a lot of people. Unfortunately this is the best I can do at the moment, I think a lot of your work is simply digging into your car and tracing the circuits looking for faults.

It sounds like someone who had no idea what they were doing just started hacking up wires in your car and threw everything back together so they could sell it. Do yourself a favor and get a decent digital multimeter, it will greatly help you in chasing down gremlins and is an invaluable tool in the box for any electrical troubleshooting.

__________________
TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

Oh, and head over to w124-zone.com and join up there, Ps2cho has the manuals online if you don't have them already.

__________________
TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

I'll pull the front door panels when I get some time, have a look at the locks, and see what I can see.

As far as the rear windows are concerned, the switches in the front console seem to be getting power, but the power doesn't seem to be making it's way to the rear doors from what I can tell. Guess I'll have to try and trace the wires, but it'll be tough finding them unless I start disassembling everything.

Thanks for all of your advice. Hopefully I can get this stuff sorted out one issue at a time.