88 735i - BC function on turn signal lever

I know this isn't a complex technical question, but I do not have an owners manual. I've never known what this function is. Nothing happens when I hit it. What is it supposed to do? Maybe I can fix whatever is not working. My name is Charlie by the way. I'm a newbie to the forum. Seems like alot of very knowledgeable people are members here, I look forward to learning and contributing here. Thanks.

Lots of information here http://www.e38.org/e32/

THis is not an uncommon thing with the E32. Right smack in the middle under the speedo and tach there is a long thin blank spot?. If it is not blank then I am writing this and wasting time. If its blank thats a screen that is suppose to tell you thinks like low beam out fog light out fasten seat belts trans program error LOL.. and a whole lot of cool stuff. If its not working you proabbly need a new cluster or just the SI board. When buying a new cluster pay attention the the color of the back of the cluster. In 88 its grey. Mileage is not stored in the cluster so when buying one how many miles it says is irrelevant if you plug a different one it it will say the same miles as it had when you pulled the old one out.