DD has both electric and air horns. The air horns had not worked since we got het, but this last weekend I decided to try my hand at fixing them. During my research I found several you tube instructional videos, and it looked easy.
No idea if the electric are stock or add on because air horn was not working. Disconnected them anyway, and began working on the air system. First thing I noticed was the solenoid for the air horn was disconnected from a ground. I reconnected it, then I took the back plates off, cleaned them out with compressed air, and shot lots of debris out the front. Then reassembled, turned DD on, and waited for full pressure on the front tank. Pressed the horn and nothing. Turned off the ignition troubleshoot everything and tried again. Turned on the coach, and got the rear tank gull, pressed the horn and psi gauge for the rear tank dropped 10psi and the horns blew! First time they've ever worked, and they sound awesome.