I hear a lot about the radio code once you remove the radio and stuff, will I be affected by this in any way by putting in an aftermarket head unit? It doesn't seem that I would but I did notice that my car's key fob quit working and I'll have to check but I don't believe my alarm is turning on or the lights not blinking anymore when I lock the doors since pulling the symphony 2 the other day to see what I was up against. any input is welcomed.\
2003 a41.8 quattro

 

Not sure if I can help but check fuses, check fob battery, and provide more details on lock/alarm (mal)functions here.

There is a portion of the alarm loop that is affected by radio presence but as you reconnected when re-installing the symphony, or you don't connect anything to it when doing aftermarket install, you should be OK IIRC. Is your system CAN-BUS? This may require additional step in installing new radio but I don't have experience with it, though I don't imagine it's hard to tackle.

On the outside, you may speculate on problems with the comfort control module, which 1) responds to signal from fob alarm antennae and 2) controls locking and interior lighting, and alarm feedback (blinking).

 

sorry, probably should have re-posted but found my answer. When you disconnect your battery cables, as everyone should when removing the radio it wipes the memory of your car from the key fob. Do not go to the dealer, they will charge you. There are a few ways you can reprogram it, most people believe you need two keys, but I did it w/ one by holding the lock and unlock buttons while the key was in the ignition and then while still holding started car, holding the buttons for like maybe 10 sec. after that I release buttons, turned off car and key fob worked fine. found a write up about it after doing some googling.

also car alarm does not activate by simply pressing lock inside the car and closing the door. you must use the key to lock the doors from the outside to activate the alarm if your not using the key fob. most people probably already knew this, but I did not.