DDM

I'm guessing the OP is speaking figuratively when he says the button says "on" or "off" and is referring to indicator lights and not the literal words ON or OFF. There are switches that will literally display the word OFF (seat memory, ESC, the AC, start/stop), but is there any switch or button anywhere on these cars that literally display the word ON in the dash or on the switch? They all just show icons, don't they? Anyway, assuming the OP is referring to a button on the left side of the headlight switch, it has to be one of three things unless it's a modified switch.

delmd92

Not gone, just too many meetings this week to get back to the thread before tonight. Literally a button that in one position it says "off" and when I push it again it says "on." It is backlit. After reading the responses I paid more attention. It does control a small light strip in the rear light cluster. Funny looking fog lights, but if that is what they are then I have new knowledge, now what to do with it. Never thought to look behind me when pushing the button. With the garage door up there was nothing to reflect the light off to notice the light and in the pitch dark of the country road I tried it on without knowing to look behind me it appeared as if nothing was happening. Even knowing what to look for it is hard to see.
I was confused after reading the manual as there was no picture corresponding to what my switch looks like, hence the question. The manual shows the rear fog light button in the bottom position but has a symbol on the button. My bottom button is as described. It appears that the mystery is solved for me. Thanks to everyone who got me the answer.

tenspeed

I used my rear fog one time in two years. That was during a heavy rainstorm on the highway. They can be used instead of hazard lights when moving to let following drivers know that you're there.

KevinGary

DB22

For those of you who have driven in the EU you will probably have seen the rear fog lights in use. It is the law for cars to have these lights in the EU and I think that they are a great idea but, as usual, the US authorities are confused by such advantages in safety and have not mandated them yet. I suspect that the US will get them in the next 10 years as the US lighting laws are between 20 and 25 years behind the rest of the world.