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90 420SEL, 00 BMW X5, 00 Lexus RX300, 01 Chrysler Town and Country
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377 Posts
Discussion Starter #1
My car has one driver's door switch meant to turn interior light on and off. There is one more sot that can house a door switch but it is blanked off.

But I have seen 420SEL's with two drivers door switches. What are the two switches for?

Related to this. My interior lights do not come on when the drivers door is opened. They do come on when the passenger door is opened. I tested the door switch and that is good. What could be the problem?
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,778 Posts
Heres the courtesy lights schematics to take a look at.....

Screen Shot 2020-07-28 at 5.13.38 PM.png Screen Shot 2020-07-28 at 5.14.07 PM.png

My SECs have several switches as well.. courtesy lamps & seat belt presenters..
Right now I am clueless as to why your car has multiple switches..

I wonder what the owners' manual has to say in that regard.

M.
 

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90 420SEL, 00 BMW X5, 00 Lexus RX300, 01 Chrysler Town and Country
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377 Posts
Discussion Starter #3
Thanks Mike. Owners manual does not provide any details regarding door switches. It is clear that the drivers side door is designed to accommodate two door switches. Some or most cars just use one switch and the other slot is blanked out. Other cars have two switches. But why? I am sorry, wish I could understand them better but circuit diagrams has always been my weak point. I am barely able to understand them. But in the attached diagram, it looks like there is mention of only one switch anyways.
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,778 Posts
Hey there Hugo,

I hear you, man.

That circuit addresses only ONE circuit to the car.. the courtesy lights ONLY.

So we need to look deeper I [fear].!
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,778 Posts
Sorry, NO looking at he US owner's manual shows a clue.

M
 

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90 420SEL, 00 BMW X5, 00 Lexus RX300, 01 Chrysler Town and Country
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377 Posts
Discussion Starter #6
Mike - two switches - both on when door opens. One is obviously for the Dome light and other courtesy lights. But question is what is the other switch for. It is obvious the factory provided the extra slot. Since it is not a switch a regular owner is supposed to know about or understand, it is not in the owners manual. The switches are on the door jamb and close or open with the opening and closing of the drivers side door (LHS or US models).
 

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Registered
1989 300SE 232k miles
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1,556 Posts
The SEL was used a chauffeured vehicle, correct? Perhaps the second switch was an illumination in the rear of the cabin, for the passengers?
 

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1985 300 TD 1981 300 SD
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433 Posts
My 81 has both switches on the drivers door, one powers the timed courtesy lamp and the other powers the puddle lamps.
 

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1986/1990 W126
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14,481 Posts
SEC has more doesn't it. Seatbelt butler arms and that.
 

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1985 300 TD 1981 300 SD
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433 Posts
Thankfully I don't have presenters, tensioners, power headrests, etc to worry about just a fried timer on the front dome lamp. ;)
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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4,778 Posts
I'm fried anyways the way things present over the last years.

M
 

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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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4,603 Posts
My car has one driver's door switch meant to turn interior light on and off. There is one more sot that can house a door switch but it is blanked off.

But I have seen 420SEL's with two drivers door switches. What are the two switches for?

Related to this. My interior lights do not come on when the drivers door is opened. They do come on when the passenger door is opened. I tested the door switch and that is good. What could be the problem?
You could try some experiments to find the answer.

With the door open, engine off, key off, note what happens when you push in each switch.

Then door open, engine off, key ON, note what happens.

Then door open, engine ON, see what happens.

You could also try having the door open, manually depress each switch, turn ignition to run, release one switch at a time.

Or, with door open and switches depressed, "lock" the door with it open (manually trip the latch) and release one switch at a time. This should test alarm.

Just try some different things.

My SEC has three door switches. I know one is dedicated to the seatback locking and one does at least the seat belt presenters but I don't know what the third does.
 

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90 420SEL, 00 BMW X5, 00 Lexus RX300, 01 Chrysler Town and Country
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377 Posts
Discussion Starter #15
Mike, I wish I could test that way. But my driving car has only one switch (1990 420SEL). It is a parts car (1987 420SEL) that has two switches. And that car will not ever run. The presence of two switches piqued my interest and led me to ask the question. I still cannot get dome lights etc to work in the driving car (1990 420SEL). I am guessing it is the flasher unit which is supposed to be behind the dash. Except I could not find it in the junk car. All I could see was a 5 inch round black AC duct there. Is it behind the duct? I do not know.
 

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1991 560sec. 1991 560sel 1969 280SL
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1,333 Posts
The flasher is one of the functions of the multifunction relay. That relay is rectangular and resides in the fuse box.
 

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1989 560SEC, 1989 560SEL, 1995 E420
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4,603 Posts
Mike, I wish I could test that way. But my driving car has only one switch (1990 420SEL). It is a parts car (1987 420SEL) that has two switches. And that car will not ever run. The presence of two switches piqued my interest and led me to ask the question. I still cannot get dome lights etc to work in the driving car (1990 420SEL). I am guessing it is the flasher unit which is supposed to be behind the dash. Except I could not find it in the junk car. All I could see was a 5 inch round black AC duct there. Is it behind the duct? I do not know.
I see what you mean. I think your best bet is having a wiring diagram expert friend decipher the factory diagram for your parts car. I'm not great at it but I'll try to take a look.
 

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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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4,603 Posts
Dividing your first post into two questions, this is about getting the dome light to work in your '90.

I'm assuming you have a known good fuse at #6 and a known good bulb in the dome light socket.

I would take a volt meter and start at the fuse box. Confirm you have power at and across fuse 6. Then pull down the dome light and make sure you have power at the black/pink (per wiring diagram MBL supplied) wire coming into the dome light package. Confirm you have power at one side of the dome light bulb holder. You're checking every inch of wire with this method in case something is pinched, broken, abraded, etc.

Next you want to make sure you have power at the brown/gray (per diagram) wire which leaves the dome light package. This wire apparently goes to the warning buzzer which I believe is, in fact, behind that 5" A/C duct. It's a pain to remove. Sorry.

If you have power so far, now check the brown/gray/red wire leaving the buzer. This wire leads to the door switch so if you have power to this point, there is either a problem with the switch (Corrosion? Poor contact?) or with its ground wire.

I think this exercise should solve your problem. Mind you, this is a lot easier to write about than to do, at least for me.

I am NOT good with wiring so anyone who sees errors here is invited to correct me and steer hugo in the right direction.

Good luck.
 

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90 420SEL, 00 BMW X5, 00 Lexus RX300, 01 Chrysler Town and Country
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377 Posts
Discussion Starter #19
Thanks Mike. The bulb has to be good. The light and buzzer (key in Ign) come on if I open the passenger door. And the drivers door switch is good too.
 

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Outstanding Contributor
1989 560SEC, 1989 560SEL, 1995 E420
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4,603 Posts
Thanks Mike. The bulb has to be good. The light and buzzer (key in Ign) come on if I open the passenger door. And the drivers door switch is good too.
Okay, good.

I'd suggest you swap the driver's and passenger's door switches anyway. If the driver's door still doesn't trigger the light and buzzer, you must have a problem in the wiring to the driver's switch, at or after the warning buzzer, right?
 
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