I just went through all of my fuses and mapped where they were at. Not one is marked for the back up alarm. If no one answers with a location, you can do as some have and just add a switch in the engine bay or just add an inline fuse by the alarm.
I would love to have a switch on the dash, but haven't been motivated enough to run another wire back there.
Don & Mary
2019 Newmar Dutch Star 4018 - All Electric
2019 Ford Raptor Crew Cab