I had a C230 and I know how reliable they are so this should just be a matter of finding a bad fuse or relay or loose wire.

First thing is you should have two fuse boxes, one in the trunk and one on the engine compartment. When you take the cover off the fuse box, stuck in the inside of the lid is a paper listing fuse resistance and location (all by numbered location) look to see if one fuse has all the problem components listed to a single fuse- that's the first step.

Actually this wouldn't be a bad time to change out all your fuses.

Next check to make sure the battery in the trunk has both terminals securely attached without any corrosion on the terminals. A weal battery can reveal itself in strange ways - any battery older then four-years can be questionable.

Also if you have a rain sensor in your windshield some of the electronics for that are in the overhead light console above the rearview mirror and the horn and turn-signals are related to the alarm system so keep that in mind while searching for which fuses are involved.