9 times out of 10 it is the horns themsleves, or rather, the metal spade lugs to connect them. As you will see, MB did a dumb thing--they put them right in front of the front tires with NO shielding whatsoever. The contacts just disintegrate over time. The good news is that if you do not care about having the absolute correct original tone, you can get generic horns at a local auto zone or the like for around $10 each. They fit perfect and get the job done, meaning, they go "beep".