how the unit is?

Is there a bypass for it?

Thanks ahead of time.

Its nice. Yes, its bypassable

how is it bypassable is there a diagram?

Also I currently have a dvd w/monitors in the headrest for the rear of my truck(currently working with factory radio) does the 5900 have a video input so I can connect the old dvd player to it?

Hook up a switch so the parking brake sees on-off-on to ground, or use a relay to simulate that. Yes, it has an A/V input

good bypassable unit.