2008 hummer h2, mute nav radio?

Anyone know how I can mute the factory Nav radio? I am installing a parrot 3200 with an external speaker. I tried using a gmcss3 but this piece is not working with the gm lock pick that is already installed. The gm lock pick quits working when I install the t harness that comes with the gmcss3. So now i am trying to find a way to mute the radio with out the  gmcss3. Any info is appreciated. Thank Youmexicang

if it has a factory amp, use a relay to cut the constant power to it.MECP Master Certified Technician

ASE A6 Certified Technician