This has been covered a few times for the bedroom TV as the 2860 outside TV has the same situation as the bedroom TV.
For years, RV's had low def TV's. Coax came in...coax got split to every TV, no big deal. As digital signals became the law of the land doing this produced less than satisfactory results. We used to use a switch box, but again the signal gets split so many times that by time you got to another TV the signal had degraded. Instead, we try and feed every TV individually for the best image.
It cane be done, but not without some parts.
NO SWITCH BOX
Basically there is one output from the dash DVD player (red/white/yellow). There is no coax out from the dash dvd. So you would need to split the Red/white/yellow. One set goes directly to the main TV, the other set would go into a convertor (can get those at Radio shack). that converts the composite cables to coax cable. You can then feed that into the top coax cable of the jumper
If you have a switch box, that already acts as the convertor. Make sure everything is on DVD. On the outside TV you would turn to channel 3 or 4 with a DVD playing and then scan for channels. Again, image quality (converting composite to coax) is poor.
You'd be better off buying a $30 DVD player and feeding the TV with HDMI.
Diagram of the wiring attached.
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