As you can see in my pics posted above, the grommet is visible behind the brake boost cylidar. On the inside, it will be behind a perforated rectangle of vinyl covered padding. It sits just to the left of the brake pedal. Just use a knife to cut along the perforated line, and pull it aside. The factory grommet is oval, and more plastic, than rubber.
You will need to measure what size wire diamter you're running, and cut the hole size accordingly, THROUGH THE FACTORY GROMMET. It's thin, and stiff. After you cut through it, you'll see the edge that is left will leave a pretty sharp edge. I prefer to use an aftermarket plastic firewall grommet, so you don't risk your firewall (or factory seal/grommet) rubbing through your wire insulation. Again, refer to my above pics. You'll see what I'm talking about.
Your wire should then feed right to the factory wire channel without any trouble, or interference.
