One problem related to horn assembly has been reported for the 2008 Mercedes Benz C350. The most recently reported issues are listed below.
The rear passenger tail lamps are dimming to about half the normal strength. The bulbs are all fine, but I am getting notices on the dash that the lights need to get checked. I checked the rear light harness and it appears the electrical connector has melted so that it can't be removed from the component that actually holds the bulbs. I am concerned that this might be a fire hazard. The electrical failure also seems to be affecting the horn. There are two horns on this car. One is on the drivers side and one on the passenger side. The passenger side horn is not functioning. It appears like there is weak to no electrical power on that side of the car. This is extremely dangerous too as I can't warn other cars on the road if needed.