I have a '95 E320. My dash light that indicates an exterior lamp failure came on yesterday while driving. As soon as I could, I checked through all the lights. All lights functions normally. I checked the fuese, and they are all OK. But an interesting thing was found. The right rear bulb assembly unit lacked the base contact for the fog lamp bulb. It doesn't appear to be broken, it looks like it was never there. No bulb, no contact. The left rear assembly was complete and intact (the left rear fog lamp functions normally). The indicator light comes on when I: (1) shift into drive or reverse (I have to press the brake to get out of Park), or (2) without shifting out of Park, I can depress the brake and activate the turn signal (left or right). I have two questions. First, is there an indicator detection unit that could have failed? Second, why did it not come on before when the fog lamp socket was faulty? Thanks in advance for any hints you can give me.

The rear fog lamp is always only on the left side. There is never one on the right.

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Bill Wood - Webmaster
MercedesShop.com, LLC

Check your brake lights first (all three),have some one help you to step on
brake while you check it out.
Fog lamp only at left rear side.

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MB STARS Master Guild Technician,12 years MB tech
5 years independent shop owner

I sometimes think that the dash light has ESP or a crystal ball. The dash light on my '94 E320 also lit up a few weeks ago, and, like you, I couldn't find any burned out bulb. The dash light didn't come on the next few times I drove the car, but a few days later it lit up again. This time there _was_ a bulb burned out (one of the rear side marker lights).
I believe the indicator light on the dash lights up if it sees an imbalance in the resistivities of the lighting circuits. In your case it may be a bulb with a higher resistance on the verge of failing. Are any of your lights unusually bright?
The left side only bright tail light was explained to me as a safety feature to prevent people from rear-ending you while passing you in thick fog.

John M.

Don't forget to check the licence plate lights as well.

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Tom Garvin
MBCA Toronto Section
1989 420sel

The lamp warning circuit uses circuit resistance as a way of testing all the lighting. Even changing a lamp with a different style base, ie. brass vs. steel can make the light come on also.

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