On past trucks, the fuse for the 7 Way constant was included in the packet with the harness for aftermarket brake controllers.
May want to check and see if it's left out.
Internal Power Distribution Center
The Power Distribution Center is located under the drivers side instrument panel. This center contains cartridge fuses, micro fuses, relays, and circuit breakers. A description of each fuse and component may be stamped on the inside cover, otherwise the cavity number of each fuse is stamped on the inside cover that corresponds to the following chart.
Cavity/Cartridge Fuse/Micro Fuse/Description
F01/30 Amp Pink/–/Trailer Tow Receptacle
F25/40 Amp Green/–/Mod Integrated Trailer Brake