There are two different controllers, the early style and the later style. The early style usually used on the 6.9 has the controller screwed into the engine(the brain part of it) and it controls the solenoid on the fenderwell. I have never switched this system over to manual, but from what I understand you need to find a small hot wire under the dash somewhere, run through a momentary switch, and then run another wire from the switch out to the fender mounted solenoid. The switch will fire the solenoid(small wiring) and the solenoid will then do the heavy work(the larger wiring). To fire this solenoid, that must be the purple wire they are talking about.
The later type controller is mounted at the rear of the engine, and it's a combination of the controller brain and the solenoid mounted to one piece. This is the type I have, and to convert it you take the white wire loose and tape it off, and then add a wire where the white wire used to be, run it into the cab to a momentary switch, and then run a ground wire to the other side of the switch.