I own a ML430 (year 1999) and my horn also stopped working. I have checked the relay to make sure that it is clicking, and the 20 amp fuse is Ok. My question is where are (is) the horn located on ML430. I see one right on the firewall next to the coolant tank, but after reading this thread , it seems that the ML has two horns. What is the location of these horns. Any help will be greatly appriecated.