Idiotic? But your entertainment system is the screen where the rear-view backup camera gets displayed. You need the computer controlling the transmission to be able to tell the computer controlling the entertainment system to start displaying the camera feed. Now they're wired up. And I think you'll find that by the time you hit every use case (safety interlocks that prevent changing GPS coordinates while the car is driving, vehicular speed being to augment the GPS in tunnels, etc) you'll find that just about everything gets connected somehow.