One problem related to horn assembly has been reported for the 2001 Mercedes Benz S500. The most recently reported issues are listed below.
We purchased our 2001 mercedes s-500 used. Everything ran fine. After running it through an auto carwash with a under body spray, the electrical system went haywire. I noticed that the front passenger floor was soaked. Electrical malfunctions included non functioning locks, windows, air, all lights flickering, seat controls, horn, hazard lights, sunroof, dash control, virtually everything electrical. These malfunctions occurred while the car was in motion and while parked. When we turned the key off and removed them, the car continued to run. We disconnected the battery and the car continued to run still for an additional 5 minutes. After doing some research online, we have discovered similar complaints with the same situations including passenger floor being soaked resulting in electrical faulting. (see attached picture) complaint below mentions a stupid repair kit at owners cost meaning mercedes is aware of this dangerous possibly deadly fault in their vehicles.