There are several unused holes with rubber grommets already waiting...
Roughly under the steering column. I had a bank of about 6 together with rubber grommets/plugs. I just took a metal coat hanger with a nice point on it and poked it through from the inside...then duct-taped the end of my 4ga to it from the engine side and pulld it back through. Need a little dish soap for lube
do not go through firewall.. there is a better way <more>
If you dismantle the drivers side under part of the dash (3 bolts) then you will find a power distribution center with 6 ports.
This power dist center comes straight from the battery using heavy guage wire..depending on your options some of the ports will be full but its a great place to tap in for power for amps or whatever..its capable of feeding 8guage cables etc.
It makes it perfect cuz you never have to drill through the firewall or mess up sealing grommets that come through the firewall.
i've used that already for sending some wires down from the battery. however, i hate having to remove the ecu box (wipers, etc.) because its a pain, not to mention the antenna wire is much thicker than the hole i've drilled into the ECU box already. additionally, the wire will be passing into the area behind the glove box, so it seems silly to route it all the way to the other side of the car and back. i'll let you know if i find another way!
SIG STARTS HERE
2003 Audi A4 Avant, Black/black
3.0 V6, Sport, Manual
"Mods": all-round tint, 35% front, 20% rears; sedan sport rims; clear corners; yellow fogs; V1 hardwire/concealed display; XM Commander headliner install; emergency lights/radio; Pioneer AVH-P4000DVD with stock Bose system