Either the DVD player has "exposed" RCA type jacks or an HDMI connector that will need to connect to one of the the Television's input connections (most Televisions today have several), or, this DVD was perhaps already pre-wired into the wall, and the connections from it to where ever the television mount location would be found.
Did your X18D have a "pre-determined" Television mounting location? In some cases, the factory placed a wall or ceiling mount plate with antenna/cable/DVD connections that are pre-wired.
2015 Jayco Jay Featherlight SLX16XRB (TT)
2007 Ford F150 Tow Vehicle (TV)