In a tight spot
I just did this on my 2000 Accord 4 dr sedan and could not believe I was lucky enough to get it with the first test hole. It's like threading a needle with a wet noodle. There is very little room for error because the area that is single wall was so small. Here's what worked for me.
Looking from the engine side of the firewall with a flashlight I found a small recessed area next to the steering column. On my car it is behind a bent section of the hydraulic brake lines. This small recess area (appx 1" x 2") is where there is a single wall.
The trick is... finding the small area from inside the car. I used a tape measure to calculate how far down and to the left the hole needed to be from the steering column. Then from inside the car I had to remove the steering column lower cover at the floor. This allowed me to apply my calculations using the steering column as a reference point as to where the single wall area was. This was difficult because the steering column passes through the firewall at a double wall area, so there is some eyeballing involved.
If your firewall layout is like mine be extremely careful drilling near the brake lines. I used an adjustable depth bit adjusted to 3/16", but you may be able to drill carefully if you think you can control how far through you drill. Maybe a block of wood behind the brake lines, but not much room for that.
Once I successfully drilled the test hole, I enlarged it with the correct size bit. Then from the engine side of the firewall I had to bend the brake line to the side to allow access for the cable to pass through.
Hope this helps,
Please post back with your results, this may help someone in the future with the same concern.
'98 Gulf Stream Sunsport 325, 7.5L Banks Power Pack, Koni FSD's, Air Bags, ReadyBrute Elite,
2000 Honda Accord