Sorry for the delay in replying but I have been away on business with no internet access.
From memory. The screen should have the following cables.
A Yellow/Red/Black or blue set probably tapped together. These are the power supply cables from the back of the DVD player. You would need to splice the cables from your additional screen to these somewhere in the system. You may have to uprate the fuse slightly that the original screen supply comes from to allow for the additional load from the second screen. You will need to check the power consumption of each screen to do this and add them together to get an idea of what fuse rating is required.
There will also be a video coaxial lead and a left and right sound leads. These are the same as you get with camcorders and VCRs. Not sure how you can connect these as I do not know how they terminate at the screen. It is possible to put Y connectors at the DVD player end to overcome this but you would have to run the cables all the way from the screen to the player.
Hope this helps.
Drop me an email if you need any more help. (use my profile)