03 expedition factory dvd w new head unit

How do you keep the factory overhead working with an aftermarket h/u.  the factory deck has beed destoyed because of stuck cd's inside and I have no way of determining which wires are used to power up the factory overhead/dvd. I have a small 4pin harness and a larger 20 pin harness colors are as follows:

4pin harness:

GREEN/ purple, black, BLACK/ orange, RED / black

20 pin harness:

brown, blue/red, lt. GREEN/ black, blue, grey/black, lt. blue/red, black, red, black, white, lt.green.

any info is appriciated.

On the large plug:

Pin 5 Lt. GREEN/ Black:  power this as Ignition, this turns on the Overhead.

Audio:

Pin 19 White: Audio L(+)

Pin 20 Lt. Green: Audio L (-)

Pin 17 Red: Audio R (+)

Pin 18 Black: Audio R (-)

Audio lines are low level so connect RCA ends to them and connect them to your aux input on the new deck.