Jpick

it was the wiring. Thieves cut it in attempt to break in and steal truck or contents

As a follow up, my horn wire was cut. Would assume a pro that got scared off. They likely cut the horn, went to break in at the lock and the lights started flashing since the alarm uses both horn and lights. I relocated the two horns on my 2021 over in behind the headlight and had to use insulated alligator clips to just catch the 1/4" of a wire stubs they left because they cut it up above the plastic wire sheathing that is to protect the wires. Ordered a new connector for $9 off amazon (came from a GM dealer) and have it on the list to fix it. GM needs to think about fixing this. My horns are still loud enough and pretty unobstructed where I relocated. But they can no longer be accessed or seen through the front grill. I have a 2021 GMC Sierra 1500 Denali with 3.0 diesel

Not yet, because the horn quiting seemed related to the attempted break in and the door handle. TRhe fuse is all I checked. I haven't checked the relay yet either. Thanks, will check the easiest thinks first. And the wire to the horn is a good idea. they might5 have cut it if it is easy to reach

Same thing happened to me this week while parked at a hotel. Culprit obviously tried to use a screwdriver or something and now no horn. DIC said Theft attempted. DId you wind up going to the dealer or figure somethingout yourself?

I have had this happen since I got the Truck new in Dec 2020. It has to be related to the camera in the rearview. Sun and also ice have caused mine. Due to the location, defroster does not knock the ice off there at Rear view mirror assembly. Discovered the ice issue when the ice had set in overnight and we headed south and the roads were clear but the windshield was not yet. I dont think there is an issue to fix. Just going to deal with it