There are holes with grommets on both sides of the firewall on my 6th gen, I'm sure it's the same on your car. I used the passenger side since it's closer to the battery...it's under the under-hood fuse box. Use some stiff wire, tape your power wire to it, and shove it through the grommet, you'll be able to get the other side under the dash, if you have a passenger side interior fuse box, removing that cover will give you more access under the dash.