One problem related to horn assembly has been reported for the 2004 Chevrolet Silverado. The most recently reported issues are listed below.
When the outside air temperature gets approximately 75 degrees, especially over 85 degrees, the vehicle's horn will not operate. It has been a problem since the vehicle was delivered new. It has been to the dealer for repair 3 times. Each time it is claimed to have been fixed. Yet, once the outside temp goes up the horn will not work. After some time while driving it may operate intermittently. It is a serious hazard since, during warm weather, it is likely to not work in an emergency. On at least 5 occasions it failed during an emergency when I tried to use the horn. I registered a complaint with general motors (file no 1-413956517) but they have been non-responsive.