The park cable input goes to the antenna amplifier which also serves as a switch between the cable input and the antenna input. For watching cable, you need to turn off the amplifier. It is a little black button on the amplifier face plate. Green light on indicates amp on. Green light off (amp off) for cable.
If you don't know where the amplifier is, follow the antenna wire out of the TV back to its source. The amplifier will be where the wire attaches to the wall plate.
2012 Forest River Sunseeker 2300 Chevy