if the sound is INSIDE the cab, then it should turn off backup warning when you plug the trailer in. works on my 12. my 08 did not have this
this auto shutoff only works for trailers with electric brakes.
I know you can manually bring up the panel to enable/disable the backup sensor warning.. just don't remember how to get there without walking out to my truck
if the warning is OUTSIDE the cab, it does NOT turn off when the trailer is attached, and there is no manual on/off switch (to prevent you from disabling if u are supposed to have it).
you would have to add this switch yourself. I haven't seen anyone do this.. maybe asking in the Ford-trucks.com/forums/forum205 (6.7 superduty, 2011 and up) would find some help.