First off... what gauge wire are you running? That will change how you'll have to route the wiring, the bigger it is the harder it is to route without drilling holes in the firewall or running it under the vehicle to the back.
I'll tell you how I ran my mom's installation on her 96 Bird... We used 8 gauge wiring, so it wasn't that big, but 4 gauge may work this way as well. I ran it into the front driver-side wheel well, ziptied it up to keep it under the splash shield (it helps to take the wheel off and the splash shield out). I then ran in through the grommet that the hood release cable goes through. Once it's inside, grab it, and hide it under all the trim under the dash and under the door trim piece. Pull out the bottom of the back seat and run the wire into the trunk.
If it makes sense, it works pretty well and nothing is damaged (no holes drilled) which is how I prefer to do things. You don't see any of the wiring.
Nick