I know you guys have already sorted this out... but screw electrical tape. You don't need to go find a grommet anywhere to fit the hole assuming your stereo is a permanent installation... Just get a drill bit a little bigger than the wire (because rubber stretches and closes back down smaller than the hole you drilled), drill out the factory plug and pass it through to make your own grommet. It's a lot neater that way, and equally as waterproof. That will keep it from touching any bare metal or cutting any insulation. The grommet is a real bitch to get back in there if you put a big wire through it because the ventalation duct is so close to the hole on the other side.