i have a sony xplod cdx-L550x and i hook it up. I did everything right. And when i play a cd on it it wouldn't work, but i can hear the bleeping noise. And the radio doesn't work also. IT says ATT. Please Help Me.
att switches on my amps are used when a source output higher than 4-5volts is used. e.g., if your HU is 6-10volts out, then the function allows you to compensate for it on your amp.