Alarm & Radio Install. Factory GPS issues

[rnaz1017]

Hi, I have a 2004 MZ3 with factory Navigation and the factory stereo with 6 disc changer. Looking to upgrade the stereo with the stereo from my old car that I'm getting rid of. Anyone have any advice on installing the new radio? Clarion NZ409 single DIN. My only real question was anyone ever tried to hook up their aftermarket HU to the steering wheel audio controls??

Also I have a VIPER 5901 I have to install from my old car into this one...ugh...so much money lol.

And last but not least my factory GPS works..but it'll go blank or the screen will have a red tint to it and then go blank...no idea why. But 10 times out of 10 if i hit the passenger window switch and open/close the window slightly it always comes back to normal...my fearnce install the new radio and mess around in there it might not be that way...ANYONE ever had problems like that for their factory GPS??

Thanks for to the help, its my first post and my first week with the car. It's great car!