Matt -
Referring to this article, and as mentioned by Lyle in the previous post, given that you have a 7-pin connector, it seems likely your 2014 Flex may be pre-wired with an OE connector under/behind the dashboard for addition of a 'plug-and-play' aftermarket brake controller (e.g. the popular Tekonsha Prodigy or similar) with a simple adaptor pigtail. That 'adaptor pigtail' would connect to the controller and then plug-in to the connector already existing under/behind your dash.
If that's the case then adding that sort of controller would be very easy, not requiring any additional wiring in your vehicle. You might check with your Ford dealer or a competent hitch installation shop to see if that's the case.
Good Luck!
That was the case in my 2004 f150 when I bought it the wiring and relay were unopened in the glove box, the relay was installed and the tekonsha plugged right in and worked. Took an hour. Check that the f150 your borrowing has the built in brake controller on the dash, most new ones do.