I have two W124s and noticed on both sets of rear lights that the driver's side has an extra bulb. The passenger side has the symmetric hole for the bulb, but it's not wired.
Any idea why MB designed it this way?
Thanks,
John
1994 E320 Wagon- 127K miles
1995 E300 D- 141K miles

That's your rear fog lamp.



-Jason

__________________
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.

I'm not familiar with the model, but a good guess would be it is for the european configuration tail light (brighter than usual) that is illuminated in foggy conditions for better recognition of your vehicle by traffic approaching from the rear. Do you have an extra switch for which you have not yet found a purpose?

You turn it on by pulling the headlamp switch out to the 2nd click.

__________________
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.

Yes. Early W124 did not have this style switch though. But the spot for the bulb is there.

__________________
http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

I appreciate the feedback. After your answer, I was able to google the info below.
http://www.benzworld.org/forums/r171-slk-class/1265137-how-many-rear-fog-lights-there.html

http://en.wikipedia.org/wiki/Automotive_lighting#Rear_fog_lamps