Here is the grommet. The cockpit side of the grommet is much bigger than the wheel well side, so I had to pull it out from inside the car. I used a knife to cut a X into the grommet and then put it back before pushing the wire through.
Thinking back, it would be easier to push wire through if the grommet was installed backwards with the larger side towards the wheel well. In my case, the grommet fell out a few times when I push the wire in from the wheel well.