first of all the in-dash isnt connected directly to the parking brake, its connected to the parking brake light on the dash, the two wires are soldered togeather. Yes i beleive it is a law, i beleive in all states it is mandatory for an installer to connect it to the parking brake wire, but most places if you ask them too they can convieniently "forget" to connect the wire and they just leave it dangling under the dash. If you have a pioneer indash and you are planning on trying to play dvd's while driving, forget it they have motion ensors so it won't work. The bypass only works on some models. Some newer models such as the clarion vrx765vd unit recognise when it is grounded directly to the chassis and shuts down the video feed and a switch needs to be put in the line in order for it to work. sorry for the long post just trying to answer your question