ptcruiser

I have a DVD player as part of my after market radio. It has to be connected to the parking brake to function. It can be defeated by a small series of steps, but I don't know where the relay is.
For common sense reasons, I am not planning to watch it while driving, but it would be nice for a passenger on a long drive. The screen swivels, so it would be out of the drivers sight line.
Anyone know where it is?
Thanks for any input