The Wall plate is a multi function device, there also should be a 3rd port (TV-2) on the back.
But here is how it operates. And a suggestion...
You have a 12 volt outlet (Basically useless)
A switch
A light
And an antenna connection (TV-1) on the front
Switch on.. It suppplies battery voltage to the antenna up top (On the roof) where the booster is located. And SELECTS the antenna as SOURCE.
Switch off, it does not pass power to the roof. and selects CABLE as the source.
(FOr both TV-1 and TV-2 I might add.
Suggestion.. Replace it with a SENSAR PRO. Fits the same opening but you will have to do a bit of work to connect TV-1.. All the same functions as above save the 12 volt outlet.. and a bunch more
Adjustable gain 2nd pre-amp
Signal strength meter
Scanner
Audio feed back
And it still selects CABLE if you wish