Standard Winegard interior wall plate that is supplied with Winegard antennas.

On the front of the plate is:
12V cigarette lighter socket - to provide power to your TV
F-type coax (male) plug - the antenna output which you connect to your TV's anntenna input
Booster switch - to turn on/off the booster to the antenna

On the back of the plate is a circuit board. There are 3 inputs:
Antenna input - from the main antenna (normally a roof mounted Winegard)
2nd TV - you can run a coax cable from here to another location in your van. (It acts like a splitter)
Coax input - this allows an additional INPUT into the system. In most cases this connects to an external TV socket on your van that is used in caravan parts in low-TV-reception areas. The antenna signal coming into this line is available from the plug on the front of this wall plate, and also via the 2nd TV output from the plate.

People need to replace this wall plate when either the booster or any of the connections fails, and prevent signal getting to your TV.