I have been working on the same thing on a 2018 Southwind.
Fuse 8 in the power distribution box and fuse 13 in the coach fuse panel control the brake controller feed which is the center post on the trailer connector, but a controller needs to be installed under the dash for a trailer brake to have power to the post. A response on an IRV2 forum stated that Ford does not actually provide power to the center post, it must be added by the RV manufacturer or the end user.
I have so far have found this to be true. To have power to the center post for toad power a wire must be installed.
I plan to run a fused wire direct to the battery from the center post and ground post of the trailer plug.
15 amp is recommended.