I have a 1996 e320............ I noticed that the taillight where the backup light is located does not burn? When I checked it an the left the is a bulb but in the right there is not one.......... Note the backups work fine
sugguestions

Those are your rear foglights. They shouldn't be on unless it is really foggy as they are really bright and annoying. Most places in Europe only use one on the left side. When you pull out the headlight switch knob to the second position it turns on the rear lights, one position for the front.

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Fourings

84 Audi Coupe GT with Turbo engine, EFI (buh-bye CIS), Jamex seats, Koni's/H&R's, e-code lights. 210k and counting.
1992 Anthracite 400E, 161k, "Grey Ghost".
1986 VW Quantum Syncro, 192k, gone to the crusher in the sky.
1989 300TE 172k. (Was mine, now also Mom's car)
72 280SE 4.5 (Mom's car)

It's great for times when someone thinks that their high-beams are appropriate for your rearview mirror.

Oh, and in bad weather.