I lifted the following from my build thread showing the hole and routing I used for my ethanol content analyzer hook up
A hole on the driver side firewall with a plastic plug.
Once the plastic plug was removed there was foam about 1" thick behind it. After several trips back and forth to the other side of where the hole should be in the cabin to make sure it was feasible I took a pick and penetrated the rubber backing behind the foam.
The other side of the hole from the driver side cabin. Here's a shot with the tip of the pick barely peeking through.
I hand twisted 16 drill bits through the hole until I could fit a 0 gauge cable through it. There's less than 1" between the bundle wires and the rubber backing that has a new hole in it.
The new hole with a grommet in place.
Next I took a piece of 8 gauge wire to fish the Zeitronix Ethanol Sensor Harness through the new hole.
The new harness making it through the new hole.
Making it through the firewall.
Kind fuzzy, but it's a shot of the harness from the ethanol sensor to the hole in the firewall.
Another angle.
Next was to route the new harness over to the passenger side. I used an 8 gauge wire used to fish the harness through to the other side behind the center console. hmm... I just noticed I still have the protective sheathing on the gas pedal.
The harness in it's new home on the passenger side behind the glove box.
And a shot of the harness in it's final resting spot on the driver side.