On my 2007 ML 500 the horn will go off while driving. Sometimes it will stop on its own and sometimes I have to stop the engine to get it to stop. Took it to our local MB dealer in Midland, TX and they could not figure it out. Of course they could not get the horn to go off while they had it.

 

the air bag usually needs replacement. the contacts for the horn are incorporated into the aibag assembly. if i were you i would just pull the fuse for the horn or unplug the horns, i dont recommend it for safety reasons.on your ML the horns are behind each fog light if you have them. youll need to lay on your back to see them. it is a possiblity you could need a new steering column module in the steering column

 

Thanks for the suggestions. I did unplug the horns for a temporary fix. I'll check the airbag and steering column module.