There should be a white wire (I believe its white) in the radio harness, that is the turn-on circuit for the amp. The amp should have its own power and ground coming from the factory harness, but just needs a signal from the headunit to tell it to turn on.
__________________ -There are 10 kinds of people. Those who understand binary, and those who do not.
-If we ever forget that we are One Nation Under God, then we will be a nation gone under...Ronald Reagan