560 sel courtesy lamp trouble

Hello experts!
I am stumped on this one. Here are the details:
When opening the driver door, the courtesy lamps do not come on. The drivers power seat will not work either. When you turn the key on, the
power seat will work, but the courtesy lamps still won't light when drivers door opens.
With the key off but in ignition, open the driver door and the buzzer sounds. Leave on the lights and open the door, the buzzer sounds.
If you open the passenger door with the key off, the courtesy lights all come on. The drivers power seat as well as the passenger power seat now work, as long as the door passenger door is open.
I checked for voltage at the drivers door switch. There was none. I traced the wire from the door switch to the buzzer. The wire is good. I suspect the buzzer module has failed, but before I spend 80 bucks for one, I wanted to see if anyone had any ideas.
Thanks!
Ken
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What year is this? (schematics change from year to year).
You're in the right place though. First thing I'd so is replace the fuse that controls that circuit. Sometiems that maynot work even though they're not blown; it's a good idea to replace all the fuses actually, eevry 5 years or so (yeah I know how niuts this sounds; fuses are cheap your time is not).
Did you check both drivers door switches?
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Richard Sexton wrote:

It is a 91 560 sel. There is only one drivers door switch...
I have gone through the schematics. The common item seems to be the buzzer module, but I have not tried to trace back any farther. The only fuses I have checked are the ones under the hood in the main box. The power distribution for the power seats and courtesy lights have a common source, and they get power from the accessory side, as well as a always hot side. Since everything powers up in the drivers door when the passenger door is open, I assume the door wiring is good.
I appreciate any help!!
Thanks!
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Weird, mine has 2.

If the pass. doors makes it work it can't be the fuse. Have you tested the driv. door switch by connecting one side to a known good workig ground, like the -'ve battery terminal. Those switches are almsot always the problem, take it apart and clean it anyway (takes 5 minutes).
Have you checked for voltage at the output of the buzzer module?
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Richard Sexton wrote:

The buzzer module goes dead when you unplug it, so I will have to find my trusty voltage checker with the sharp probe to pierce the wires. According to the schematics, I should have 12 volts at junction point 5 on the module.
I did notice the empty blank for another door switch. I wonder why I have only one... I seem to have all the options except the orthopedic seat. Is yours a 91 560 sel?
Ken
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300SD, 83.
It seems unlikely MB would leave a hole there, they usually plug them up. Are you sure there shouldn't be a switch there and maybe it got bashed inside the door? WHen did this stop working? What does the schematic say?
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Richard Sexton wrote:

Oh no, they put a very nice, painted plug in the hole! :-)
Schematic shows one switch per door. I don't drive the car much anymore, and seldom at night, so it might have been broken for a few months before I noticed it. I also replaced the door light fixtures and bulbs. I noticed on the drivers door the wires to the light fixture were very tight and left very little room to work it out to replace it. I am guessing the + lead to the fixture shorted on the door while removing it and blew the buzzer module on that circuit. No fuses blew. So after replacing the light bulbs and fixtures in the doors, I noticed the trouble. But it might have been this way before I replaced the fixtures since I was not driving it much.I was replacing the fixtures because they were brittle and one of the back door fixtures would no longer stay in the door. But I bet a buzzer module I blew it removing the drivers side fixture. I have no idea why the wires are so short on that fixture, but I suspect someone pinched them in the door panel during speaker upgrades...
I am going to go ahead and replace the module this weekend. If it does not fix it, I have a spare... :-)
Ken
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Some of these switches have more then one set of contacts in them...
I think this sounds more like a switch problem then a buzzer module problem. I would pull the switch and clean it first. If that doesn't help, examine the wiring issues mentioned.
You can try the buzzer thing, but I bet that's a red herring.
Marty
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I agree. When I repaired window regulator on the drivers door I shorted those courtesy lights eight ways from sunday. The buzzer module still works even if that fuse is blown.
If it's a bad ground at the switch you will not measure 12V at the hot input if you rely on the ground being grouns which is why I recommended using a long ground wire that goes back to the battery to check for 12V att he switch.
I'd clean the switch on principle anyway. It's 15 years old and they get curdded up badly. I'd shoot it with brake (trichlorethylene) cleaner.
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Richard Sexton wrote:

I will give the switch a good going over, but it does work. And like I said in a earlier post, when you open the drivers door with the lights on, the buzzer sounds. Same if you leave the key in the ignition, the buzzer sounds when you open the door. The switch only has 2 connections on it, one for the 12 volts, one for the ground. I took it out and checked it for continuity, and it was good. I will run a separate ground wire to be sure...
Thanks, Ken
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