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Discussion Starter #1
My dome light along with the courtesy lights on the bottom of the doors are no longer coming on when I open the drivers door but they do come on when I open the passenger door.

Obviously this is a problem with the door switch. Now my question is which door switch controls this? The bottom or top one? I don't want to take the wrong out out unnecessarily.
 

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huh, my w124's only have a single door switch, I'm pretty sure?!?

the control circuitry, however, is kinda complicated. see page 69 (labeled 128) of this PDF for an 1988 300E...

http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/ETM.pdf#page=69

looks like the left door switch goes to the N2/4 "warning module", which has a diode in it so the right door doesn't trigger the same circuits. the position of this relay is shown on page 245 (labeled 240) figure 4, which the legend says is 'behind right side of instrument cluster'.
 

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They both just pull out of the door jam, no disassembly required. I believe one is for the alarm and one is for the curtesy lights.
 

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huh. my 1990 has only 1 switch, but its a 300E2.6, and might not have an alarm.

my 1993 has only one switch and I know it has an alarm, but in 93 they probably changed it.
our 94 also only has one switch and a (disabled) alarm.
 

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Probably the overhead courtesy module, which is not re-buildable....has at least one IC chip. I had those same symptoms before and more. I put a JY unit in there when the last one fails.

Kevin
 

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Simple test, take a switch from the working side, and swap it to the side that doesn't work...
 

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Discussion Starter #7
huh, my w124's only have a single door switch, I'm pretty sure?!?

the control circuitry, however, is kinda complicated. see page 69 (labeled 128) of this PDF for an 1988 300E...

http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/ETM.pdf#page=69

looks like the left door switch goes to the N2/4 "warning module", which has a diode in it so the right door doesn't trigger the same circuits. the position of this relay is shown on page 245 (labeled 240) figure 4, which the legend says is 'behind right side of instrument cluster'.
 

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Discussion Starter #10
So I'll be testing the switch as soon as I have time. If that's it I'll replace, if that is not it I am certainly not taking the whole dash apart to replace that warning module to fix this so I may look into jumping it over to the passenger side to at least have the light come on. Just won't have that warning buzzer when opening door and headlights are still on.
 
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