I had a tail light go out, so I opened the rear lamp assembly for the first time to replace the bulb.

There is a small light bulb (6W) on the outside corner of the light bar which is angled to the side of the car. I tried lots of combinations of key and light switch positions, but I never got this bulb to come on. I gave it a quick look; it appeared OK but who knows.

When is this light supposed to illuminate? I think I read somewhere its called a "side illumination bulb".

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

Whenever the running lights are on. Side marker bulb.

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Gone to the dark side

- Jeff

The filament likely has a hairline split in it, thats how they generally fail. No one seems to realize that the W123/W126 have a lamp there.

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-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

And note that they only come on with the running lights or headlights, the one side only standing lights do not activate the side markers.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Try turning the headlight switch two clicks to the left with the ignition off.

If that works, then it's the "standlicht" or "parked by the side of the road at night so you turn a light on so nobody hits you" light.

those little bulbs often get corrosion on the lamp housing terminals. i deleted mine on the drivers side when i installed my euro spec rear light. if anyone has a eurospec passenger side, let me know.