New Head Unit Installed

HELP I NEED ADVICE SIZE=7]STERO DUMMY[/SIZE] CAN ANYONE TELL ME HOW TO RESOLVE THIS I HAVE AN ALPINE HEAD UNIT I INSTALLED BUT I CANT SEEM TO FIGURE OUT WHICH WIRE IS THE POWER TO THE FACTORY AMP Y ALREADY INSTALLED A AFTERMARKET AMP AND 2 SUBS BUT WANT TO KEEP THE FACTORY AMP FOR MY DOOR SPEAKERS CAN ANYONE HELP ME WITH FIGURING OUT THE POWER WIRE TO THE FACTORY AMP THANKS