Symptoms:

1. When headlamps are ON, and I press the brake pedal, SOMETIMES (but not always) the exterior lamp failure indicator comes on and stays on.

2. If I turn off the headlamps, the indicator remains on.

3. If I turn off the car and restart, the indicator will be off.

Even though all three brake lamps were working, I replaced them (I know that the indicator can come on when a lamp is about the to fail). But didn't help.

Any thoughts as to how to troubleshoot this? Other bulbs I could try replacing? I hate to pay someone to do this....I'd rather just put black tape over the indicator than pay even an half hour labor. But it is mildly annoying.

Thanks!

PS, this is on my 300D.

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

So what happens if the headlights are NOT on and you press on the brake? I assume that all is well, though you did not say. In the case of "momentary" lamps like brake lamps, the indicator is functioning correctly when it stays on. When the headlights are ON, the taillights are also ON; it's possible that you have a bad ground at one of the brake lights so that, with the tail lights OFF, the brake light can ground through the tail light circuit. With tail lights ON, the brake light can't work, draws no current, sets off the alarm. Have you had someone stand behind the car and look as you turn lights on and off, press on the brakes, etc.?

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Yes, all is well when headlights are not on.

And yes, I 've had someone look from the outside....everything is functioning normally.

__________________
14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

These cars are sensitive to bulb wattage. Variance in non-OEM bulb wattage can cause problems. If it really bothers you, pull the cluster and remove the bulb. Otherwise look for Osram or Narva (or other OE sounding brand) bulbs of the specified wattage. Might find some in the pick-n-pull.

It's curious that it only happens when the headlights are on so maybe it's a bad ground at the tail lights.

Sixto
87 300D