Are you sure the deck is good? I mean if it has 12volts on the ignition wire, it should turn on, regardless of what's hooked up to it. If i recall correctly, the actual power is taken from the battery wire while the ignition wire (its either the yellow one or the red one) just tells it to turn on and off. To confirm check to see if you have 12 volts on the ignition wire at the plug for the aftermarket amp. Maybe the adapter harness is bad?