NavTool - Help request

[Arkaine]

Hello all,
bought a used 370z (love it) and I believe the person before me installed the NavTool. I haven't taken the dash apart yet to confirm.
As you can see from the pictures below, I have a backup camera (pic 1) and an external dvd player (pic 2) that's hooked up to the navigation system.

So my issue is (no flaming plz, trying my best to learn) that I get sound, but no picture when I try to use it.
I pulled apart the back console and I see that the left and right speakers are into the dvd player and the video port has nothing plugged into it (pic 3). I assume that red cord is being used for picture, but when I plug it in nothing happens.

Looking for some advice on what I can test before taking the whole console apart.
Is it possible the cord is bad?
Is it possible the dvd player is broke?
I would unplug the dvd player and test it somewhere else with new cords.. any recommendations on how to do this since the power is a 12v plugin?
Is there something with Navtool that I am not doing correctly to get video?

Thanks so much in advance. Feel free to PM me for conversation on this!