It was a few years ago when I put mine in, but I know I had to run most of my own wires for it. I have a feeling there was a problem with using the lights wiring.
What model is the unit? Or, do you know what the wires are you are looking for?
the interior light has constant power and switches the earths, depending on how much room you have to mount the dvd player (ive never done one before) you might be able to get a small enough relay and use the original interior light wiring for pins 85 & 86 on the relay, have the constant power wire linked to pin 30 and have pin 87 go to the blue wire on your dvd player