door wire for roof mount lcd

I've purchased a roof mount lcd and the dome lights built into the lcd housing have a wire labelled "door".  It's a Clarion OHM102.  I'm assuming this "door" wire is normally tapped into the existing dome light wiring that is hot when the doors are opened.  This is in a Jeep Liberty and the dome lights are controlled by the BCM... body control module aka car computer.  The existing dome lights fade after shutting doors, turn on w/ remote unlock etc.  I'm a little paranoid about just tapping into the existing wiring to the current dome light.  The dome have three wires.  I can use a voltmeter to figure out what's hot when...  with the BCM conrolling the rear dome would it be a bad idea to splice the wires to power the additional lights?  The wiring for the lights in the lcd housing is entirely separate from the power and ground that power the screen.  Any help appreciated. thanks

Yes they have a separate switch.  And three wires that supply them.... power, ground, and the "door".  I'm a little concerned about tapping anything bc most of it goes back to the BCM of which I don't want to fry...