On our Seneca (and our previous coach) the dash radio is powered by the house 12v system. This seems to be the typical setup as you want to avoid a situation where you run the chassis battery down while camping because you're using the radio.
The easiest way to know for sure is to hit the 12v power switch (usually near the door) and see if the dash radio loses power.
Ty & Deb Montag
2015 Jayco Seneca 36FK
2014 Honda CR-V toad