headrest monitor acting weird?

This relates to a 1997 Mercury Grand Marquis, I have a Pioneer AVIC-900BT for my main Navigation/Media player(everything works perfect). Yesterday I decided to install a headrest monitor for my kids, its a Roadview RHM 7.0G. After installng it, I noticed weird things happening, first, the headrest Monitor would not power up unless I had the RCA composites connected(red,white,yellow). Everytime I disconnected the rcas the monitor would shut off(no power). Additionly while trying to resolve this issue on the headrest monitor, apparently, my youngest daughter somehow yanked out the ground connection(-) to the headrest monitor, and yet the Monitor still powered on until I disconnected the RCAs(WEIRD), the only thing I can think of is somehow something is shorted and now the system gets its ground from or through the RCAs. Any tips, ideas, on how to diagnos, rememdy this problem would be greatly appreiciated! Thanks!  

Nothing is shorted.  The unit is grounding through the RCA cables just as you suspect.  Did she pull the ground wire out of the unit.  If so, you need to reattach it.