superduty horn sounding unattended
 

i work for a landscaping company and we have 3 F series superduty diesels that are having the same problem: at random the horn will sound and not shut off till you pull the fuse. this happened on all 3 of the following 04,05 and 06 F550 superduty with 6.0 diesel 4X4 auto. trans. what is the cause as we cant have parked trucks horns sounding at 5 am again , any help appreciated
stv357.