Well on the W126 you can turn both sides on. The first click if you turn the knob to the right are parking lights.

Also on the post 85 W126's if you pull the knob out while it is in the parking brake position you will turn the fog lights on. This feature is great, I use it all the time.

The left and right side parking lights are great if you are on a narrow dark side street. I use mine once in awhile and people seem to notice them. I wouldn't leave them on for hours though you may drain the battery.

__________________
2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200