Edit: 4 gauge wire routing on a 2012 skyactiv, no drilling.
While searching about PAC’s and LOC’s I found this method in the MazdaSpeed section posted back in 2009, figured I’d see if it worked before I drilled something to get a 4 gauge wire through the firewall to power my amp and subs. To my amazement it actually worked great, figured I’d add it to the skyactiv section because with all the hours I spent looking for a way though this method was never in the search results.
Here’s how to do it…
First (optional) get the drivers side of your car on jack stands so you can see what you’re working with. You’re looking for the steering column and the rubber grommet around it in the second picture
Next feed your 4 gauge wire down behind the battery until you can get it from under the car, you may need to reach up under the car to grab it
Once its out the bottom I held it up to the steering column grommet and had a friend mark the wire with electrical tape so I would know how much needed to be fed through the grommet. Once marked I tied a piece of rope to the wire and sent that through the engine bay to underneath the car as well to pull the wire back through.
Untie the rope and pull the wire out of the engine bay and bring it into the car. You'll be feeding the wire from inside the car through the steering column then to the battery. Find the steering column and pull the carpet out from underneath the black plastic protector. Your wire will be going through right where my finger tip is. Take a index car and fold it up long ways so it has some strength and feed it in between the foam and metal of the car as shown (This will stop the foam from binding up while feeding the wire through)
Now feed your wire through from inside the car, once you have about a foot through reach up under the car and make sure it’s not binding on anything before you feed the rest through, keep going until you hit your electrical tape mark.
Now attach the wire to the rope, try to tape the end so there is less flat surfaces to snag on things. It got snagged multiple times while trying to pull it through but eventually it will go. The second and third picture is the wire going from the grommet to behind the battery on its way to the top.
Once the wire is in the engine bay and you want to put on some plastic split wire loom for extra protection you just put a couple inches on at a time and push it back down behind the battery until you covered the whole wire and it touches the column grommet. Then pull the wire tight and zip tie and tape it off so there isn't any slack swinging around in your engine bay
Last thing to do, feed the wire up behind the plastic cover of the steering column, tuck it behind the clutch and over towards the door to start tucking the wires down the car towards your trunk
Now you have your 4 gauge wire ready to hook up to your battery and your amp without any drilling.
Like I said in the beginning, I found this in the MazdaSpeed section and was posted by “JONtheBOMB” so all credit should go to him, here’s his post where I learned this Amp/Sub install with factory radio and LOC
Since this works on Skyactiv’s and didn’t come up any of the searches on how to get through the firewall I just wanted to add this to the skyactiv section and save anyone the hours upon hours it took me to finally find a way to get through the firewall without drilling, hope it helps!
Heres a second option, and my original post, for smaller wires...
Remove glove box (Sorry no pictures of this step but can be found on forum)
Locate this clip behind the glove box and on the back side of the firewall where you’re trying to get through. It is attached by two Phillips screws and slide rails that slide out towards the passenger door. (Second picture already has blue wire I put through it)
Remove the screws and slide the clip off. Bend back the foam and enjoy the easy route through the firewall.
Feed your wire through and reattach clip making sure the foam doesn't roll up underneath it while sliding it back into place (I'm choosing to go above the ac line so the wire wont heat up, It’s the top of the two metals pipes. Found this pipe because when the ac is on it will be the only cold one)
For larger wires (sub system wires) I’m guessing that just taking a dremel to the plastic clip to allow for a little more room would work fine but seeing as I’m only installing LEDs as drls the clip fits right over the wire no problem and foam seals it up.
Hope this helps any who are looking!