+1, What Dave said.
If you want the dash radio to play DVDs throughout the coach, you're going to need to get the signal to the AV switch box. There are options.
Option 1, the "correct" way is to run wire to it. You can dismantle your cabinets, walls, and make new holes. Or you can pay someone.
Option 2 is to purchase a separate DVD player and place it right next to the AV switch box, (that's what I did, $19 for a progressive-scan Sony DVD player at Big Lots).
Option 3 is to purchase a wireless TV transmitter/receiver system, (price varies). Connect the transmitter to the dash system output. The reciever to the AV switch box.
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