Hot wheels-
Here is a link to a Google search of iRV2 posts with the terms "Newmar," "Mountain Aire" and "brake controller in them.
The gist is that the "blue wire"- if it is there- is buried in the wiring bundle near the steering column, along with the input wires to the brake controller.
Every now and then, Newmar technical support has told people on iRV2 that their coaches are not pre-wired for a brake controller, when they are pre-wired. Keep that in mind if you talk with them, or the coach's chassis manufacturer.