I wish I had good pics of the location, I've done so many cars recently and never taken a pic of the power wire pass through.
Ok, if you open the hood, and look at the firewall on the driver'* side, wait... this is where you've already looked. That IS the hole you wanna go through, there'* plenty of space, you can even fit 4Ga through there WITH the rubber plug in place.
Just leave the rubber in there, and use a coat hanger to pull the wire through, with the wiring going from the cabin TO the engine bay, that way of course you're running less of the wire through the hole.
Maybe take a pic of what you're talking about and we can see if it'* the same hole...
1999 Mustang GT - 5 Speed - Modded to hell
2004 Infiniti G35 - Loaded - 6 Speed
1998 SSEi - Black & Chrome - Dual 10" Infinity
1997 SSEi - White & Chrome - Rear ended, and written off.
1995 SE - Green & Gold - Given away, :(