I replaced the burned out license plate light on my 95 E320, but the dash indicator still indicates a fault. Playing around with this, I find the dash light goes away when I open the trunk, regardless of whether the license plate lights are on or not, but the indicator light lights up when the trunk is slammed shut. So there's something about the trunk closing that has to do with the dash indicator. Where can the problem be?

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95 E320 Cabriolet, 159K

What happens if you set the trunk lamp switch to the Off position?

I tried to look for the switch (cursory examination), but couldn't find it. I tried watching for response with the trunk light, but the trunk closes tight before I can tell when the trunk light is out. I did disconnect the trunk light but that didn't make any difference, dash light response is the same. The dash light only comes on when the trunk is closed tightly.

Where is the trunk lamp switch?... and curiously, why would the trunk light (or switch) have anything to do with the exterior light feature?

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95 E320 Cabriolet, 159K

Not sure if this applies, but on the older cars the yellow indicator will not shut off if the replacement bulb is not the exact correct wattage.
I had replaced a brake light bulb on my 126 once with a regular 12V.
After tearing my hair out for several days , someone here had me look into the wattage thing. Sure enough the new bulb was 12V10watts and the car demanded 12V20watts. The trunk issue does correspond to what I suggest.
Good Luck

One thing I find curious that I forgot to mention was that each of the license plate lights seem to be independently controlled with a mercury switch that turns them off as I lift the trunk lid, though this has no effect on the dash indicator.

Why are they switched to go off when lifting the trunk lid, and why are they independently switched?....... strange..... I'll never understand the logic behind some of MB's designs.

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95 E320 Cabriolet, 159K

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What ??

Don't see any of that on my 124.066 lighting schematics..
I see trunk sw S 19/8 and plate lamps E 19/2 and 3 [ R/L] , along with same circuit for High Center Stop E 21 . but no Mercury switching.

The reason I ask to test trunk sw in Off position is to eliminate possible chafing of wire in lid or at harnes/hindge pivot point

I assume you have tried the High/Center??

Thanks Arthur. When you said there's no mercury switch, I zoomed right in to the wires at the trunk hinge. I found three broken wires.

On a more troubling note, the insulation on these wires appears hard and not pliable at all.... less so than the engine wiring harness of my 34 year old Oldsmobile! I'm afraid the wiring harness problem on these cars goes beyond the engine and extends throughout the whole car!

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95 E320 Cabriolet, 159K

well, I always figured , if they couldn't take the heat under the hood, they sure aren't going to last in the trunk either. They just screwed up big time . ... I have a fried who is a Jag Tech and he says they are having the same problems throughout the whole car.

Been a Benz guy for 40 years and the unforseen things happen, but at least live up to it ..
Like I said 2 years ago.. be a shame to see a line of real pretty. lux. cars lined up in a junk yard cuz they are all brain dead.
My old 71 250 has no wiring problems and the seats still look new .. they should have made the wire harness out of MB TEX !!!!!!
Hell , if they did that , they probably wouldn't even need copper inside..