I know there are numerous threads regarding this subject but here we go....................
Just fitted a new Alpine head unit in my Z, all went well until i tried to power it up and yes you guessed it..........................................NO power at all anywhere, refitted the bose unit and all worked fine, tried the alpine again with all the connections and it turns out that the bose unit was using the radio antenna as an earth, once that was sussed out i found i had power but no sound, mmm after a bit of trial and error i found a blue/yellow wire in the new harness that when connected to a wire in one of the multi plugs (more trial and error) i found sound and lots of it. Once this was identified i only had to lengthen this blue wire and bingo we have a fully functioning head unit with Blue tooth and facebook, it plays audio from a hard drive or an sd card through usb too. Happy Days.