Not sure I understand about placement of your vent. But I'll use our 283ts as an example.
In front area I have 2 openings. Forward is a powered vent. Next is the air conditioner. Then there is a powered vent in bathroom. Last, in bedroom there is a powered vent.
If you are referring to a simple crank open non powered vent, but there are wires tucked up under the shrowd, than it is most likely pre wired for a powered vent. That it is a closed loop simply means you would have to cut the wires and wire your powered vent in, the fan switch completing the circuit.
As for the colors of the wire, don't remember mine being purple. Usually you'll find black/white or red/white.
If your unsure, try to contact Forrest River. Or. a simple circuit tester with a sharp probe will tell you if, or which wire is "hot".