Car Stereos: 2003 Chevy Silverado aftermarket deck, ready deck, chevy silverado

Question
I had an aftermarket deck installed in my husbands 2003 Chevy Silverado. It is a Sirius ready deck. Ever since install, crazy things have been happening. His horn will go off for no reason. We had to pull the fuse for it. When he turns off his truck and takes his keys out of the ignition, shuts doors and locks it, the deck will still be on. Any idea what would cause this? Would it have anything to do with the "wiring" or the "Brain" as my installers called it? I know it's kind of a repair question, but I am hoping you in all your wisdom might know! Thanks!

Answer
Any aftermarket deck installed in this vehicle would require a GM databus II interface to continue to allow the door chime and audible safety warnings to function. I am not sure if the horn system is also grouped into the databus function, but it kind of sounds like your interface isn't working correctly or something in your sat radio isn't jiving with the databus interface. The problem with the radio staying on could also indicate an issue with the sat radio or incorrect installation.  
Best bet is to take it back to the installation center you had the install done and have them look it over.