I agree with Tarheel -- the antenna selection between the Winegard roof mount and the park coax jack in the bay where the external phone connection is located will be made by the state of the antenna amplifier switch. It is shown as the block in the lower left of this diagram...
You have to have the switch in the position where the red light comes on to use the roof antenna on my coach -- maybe the same on yours as well... Often this switch plate has a cigarette lighter socket on it also, so it should be easy enough to find.
Chuck