First--disconnect the battery, then the electrical plug for the airbag. On the 126 the plug is under the passenger kick panel. This eliminates accidently discharging the bag.
Second--The 2 holes on the back of the steering wheel likely have T30 torx head screws. You'll either need a short handled T30 driver or a socket head. Screws are longer than you'll think, but the bag should loosen. Two prong electric plug pulls right out. Lay airbag flat with the finished side up. You're there, a few small screws on the metal plate and you are where you need to be.
Third--if you need to remove the wheel to fish the connecting wire through the column, it's a 10mm allen head screw. Socket with 1/2" drive breaker bar and an extension will be nice to have for this. Spare pair of strong hands to hold wheel firm would be nice. Clearly mark the wheel position before you remove it so you don't have to remove it again (and again) to straighten it.
A few tips from an ametuer--fully extend steering column and open front windows and sun roof before disconnecting battery. More space to work and the sun roof is a great place to run a work light. If you're going to do this kind of stuff, buy the CD manuals for your chassis from PartsShop. The steps will seem foriegn when you see them on computer, but make sense as you work. Worthy investment, the savings in labor cost on this job will pay for the CDs, torx driver, and allen head sockets.
Hope this helps--good luck.
'02 C230 Kompressor
'89 560 SEL "Frau BlueCar" (retired April 2004)