Keep in mind that when you stop and dry camp for a while, and switch that switch on the dash so the radio is on, that audio really sucks the juice at high volume and can run your battery down pretty quickly, especially if the battery is old and tired.
With that dash switch in the Radio position, the radio acts just like any car radio. When you stop and switch off the car, the radio goes off. With it in the Aux position in an RV, the radio stays ON when you're parked and the key is off.
It is handy to have that switch when you're parked or plugged into shore power because it allows using the radio without having the key in ACC position. I use it literally all the time because I plug the output of the flat panel TV into the radio so I can get surround sound. That way didn't have to find a place to mount one of those sound bars. Which just don't sound very good to me. I like using the big, heavy speakers that came with the surround sound system.
In my '02 Winnie, I too have a TV - Radio switch and circuit up above the dash but it's MONO for some really strange reason. They've had stereo TVs for decades before '02 but Winnie decided MONO was the way to go. Which meant the wiring to the radio was mono so I had to add my own wiring to bypass that switch and circuit.