Parking Brake Alarm Problem

I installed a new Kenwood headunit with video playback capabilities. I bypassed the parking brake video lockout safety feature by connecting a wire from the parking brake wire to the ground wire. It worked to defeat the safety feature of the headunit but now the Prius also thinks I have the parking brake engaged and beeps an alarm unless the car is stopped. Can anyone help me figure out how to trick the headunit into letting me watch video while driving but not also make the car beep at me? The steering wheel control unit adapter AX-TOY28SWC is installed as part of the setup. Thanks!

 

Thanks for getting me pointed in the right direction! I clipped the brake sense wire and grounded it from the headunit side and everything works just the way I was hoping.