More than likely your problem is due to the fact you're not sending a 'turn on' signal from your head unit to you amplifier. Usually the wire in question is colored blue, but you may also need to change the car's programming to recognize the presence of the wire (amp can also be controlled by a CAN bus command, a command your head unit may / may not be capable of)

 

Hi Fever

Does your mk 2 have a Bose system? If so your amp won't be receiving the correct signal and the car will need recording via vcds or similar to let it recive a 12v signal instead of canbus to switch the amp on.

DC

 

Same as FNchaos. I had the same with my Roadangel.

 

Search the forum and you will see this comes up at least once a week, plenty of info here. Bose is irrelevant because the standard amp works in the same way, both receive the power on signal from canbus. Nothing to do with the aerial adapter either. In any other normal setup in a car with an external amplifier it is controlled by a signal wire, normally blue, which sends a 12v +ve signal to the amp when the head unit is turned on, head unit on, amp on, simple. In your mk2 it's slightly different, the amp receives its signal from the can bus system digitally, why? because Audi, that's why. So you have two options, the amp can be turned on by the normal 12v signal wire method but this needs coding via vcds. The second and easier option is to use the correct canbus adapter that will tell the car to turn on the amp for you, you don't mention what harness adapter and interface you've used but if it is compatible with the digital amp its not going to work.

 

When you’ve got sound, come back and ask how to get a usable radio signal. Then we can go into Fakra stuff and aerial amplifiers…