So, in most states when you hook up a trailer over 3000 pounds you need to have a brakes and thus a brake controller. I got a Tekonsha, which modulates based on the deceleration rate of the coach. It connects to the coach with this cable:
Under the dash, by the steering column you will find this plug, with a cap/dummy plug in it. Remove, and connect the adapter.
I mounted my controller on the steering column, I can see it through the steering wheel:
In case you’re installing something else and need the info, here’s the wiring diagram for the coach side plug: