Apologize if this is the wrong board for this question. I recently left my b6 a4 sitting for about 3 months and had to jump it. Running fine after the jump but the aftermarket amp and sub (installed by previous owner) isn't working. No sound from it and the light on the volume control which was mounted in the receptacle below the steering wheel isn't on. Also oddly the light ring around the 12V is not coming on, though the power works.

I checked all the fuses and they are fine, any advice on where else to look?

 

Theres a box in the engine compartment which i believe is labed electrical center, or something like that. Look for something blown in there. As for the amp, check your remote connection at the head unit and the connections at the battery as the jumper cables could have messed with the connection.