i've asked a benz engineer once why the rear foglamp is only on one side. The reason is that so it cannot be mistaken for a brake light. It is on the left for lefthand-drive cars so that it is in the direct line of sight of drivers following you in the same lane. also notice the location of the bumper-mounted rear foglamp of the benzwagon.
the reason for having those sockets on both lamp clusters is commonality of parts between lefthand- and righthand-drive cars - i assume that the righthand-drive cars use the right one as a foglamp.
anyway, my 1989 190e2.6 also has an empty, nonwired receptacle, and i would like to get hints on how to activate it, and what bulb to use, which fuse will be used, or if the fuse needs to be upgraded.
Here in canada, being seen well from the rear is of utmost importance, especially during low-visibility winter conditions.
and to me, an asymmetrically-lit rear looks very purposeful - and cool.