The kit includes a large grommet for the firewall. The internal diameter is not large enough for the wires that need to pass through it, so it has to be "hollowed out". The plans suggest squeezing the grommet with a 1/2 inch socket in a vice. This didn't work at all for me, so I ended up drilling a 1/2 inch hole. It didn't come out quite circular as I couldn't find an easy way to clamp it other than by hand, but should do the job. It's now in the firewall anyway.
Note that the part number is incorrect on revisions of the plan prior to Rev 2. The part number is AN931-6-16.
