There is an American Coach Yahoo Group where you can learn a lot about your coach. Many vintage AC owners there, as well as newer models. You will find discussions of adding brake controllers there if you search the message database.
AC Owners Yahoo Group
As I understand it, AC did not begin actually wiring for the controller until 2004, but earlier models had some wiring present to make the job easier, e.g. a wire run from dash to the vicinity of the 7 pin plug. However, a previous owner may have already added what is needed.
Pin #4 is a constant 12v signal and is normally black in the 7 pin Pollak/Bargman connector. Pin #2 [blue] is for trailer brakes and should only have 12v when the controller is installed and actively braking.
7 pin RV Connector Wiring