How do I Install Dome Wiring for an Overhead DVD?

1). Remove the cover to the car's dome light and look for four wires. If you see four wires, use a multimeter to check for the constant 12-volt source. Ground the black lead of the meter and set it on the 20-volt DC scale. Touch the red wire probe to each wire, probably yellow, looking for the constant source.
2
Many dome light assemblies will have one or two bulbs but will lack all the wiring required to wire in a DVD player.auto bulb image by Edsweb from Fotolia.com

Take the dome light out by removing the two screws holding it in place. Unplug the dome light. Use the mounting plate of the video unit as a template to trace out its shape onto the headliner. The feet of the bracket should be pointing down and the arrow pointing toward the rear of the vehicle.
3). Cut away the headliner material from the marked off area using a utility knife. Be careful not to cut any wiring under the material. Place the mounting bracket back in the hole created by your cut and mark where you want the mounting bracket to mount to the crossbeam. Line up the cross member with the mark so you hit the crossbeam at center. Refer to the wiring diagram for the DVD player if you need clarification.
4
This is a difficult mount to achieve without puncturing the roof, so drill lightly and carefully.off-road vehicle image by goce risteski from Fotolia.com

Drill the holes into the mounting bracket where they align with the crossbeam, either two or four holes. Hold the mounting bracket with the drilled holes in place on the crossbeam and mark the holes on the crossbeam. Attach the bracket with short flathead screws, being careful not to penetrate the roof's exterior.
5). Use the multimeter to confirm which wires have the needed constant 12-volt DC. Refer to the wiring tips sections for which wires may change when doors are closed and/or the ignition is off. Route all the DVD wires down through the mounting plate hole and attach them in accordance to the particular wiring scheme that came with the DVD player.