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Discussion Starter #1
I have a 2019 Crosstrek and I'm trying to get 4 gauge wire running from the battery to the inside of the car.

I've found people online who have put wires through the grommet in the firewall and say that you have to make a cut of some sort on the "boot" on the inside of the car. I don't understand where they are making this cut and I don't want to do anything stupid.

Here is a photo of where the grommet comes in from inside the cabin. Where is the cut supposed to go? Somewhere on the big tube directly connected to the firewall? Or at the juncture where the little tube branches off the big one? I'm spitballing because I have no idea. I just don't want to accidentally cut any wires.

Thanks.
 

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It's tough to reach but I just took a scalpel and and went through the boot as close to main harness as I could get- slice carefully right beside it, not into it if that makes sense. You have little room to work there and likely won't be able to get it in the juncture so just keep it close to main harness and you'll be fine- you just don't want it "rubbing" on the edge of the firewall. You'll want to lift the little rubber flapper tab water guard thing up out of way and you can get a little better. Just take your time, you can "feel" it go through the boot and you'll know when enough is enough. My ethernet line is pretty soft, your 4ga wire should be heavy enough on its own but if not I ran a piece of solid heavy bailing wire through my slit first which I had secured my ethernet cable to, then pulled through from the inside of the car. With a light you can see exactly where you came through the big grommet at, and route the line accordingly under the dash from there.

Best of Luck,

Mike
 

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Discussion Starter #3
@'05TJLWBRUBY Thanks for the response. Sorry, but I don't actually know what a "boot" is. Nor do I know what you mean by the main harness. Am I making a hole at the base of the big tube where it touches the firewall?
 

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It is difficult to see and tough to reach-look at back of engine and find all the wires that are bundled together- the main wiring bundle or harness goes through your firewall through the boot into the inside of the car. It's not a tube, it's a wrapped wire bundle that goes through a soft rubber protective boot to seal the gap. You don't want to cut into the harness itself, you want to cut just beside it through the rubber boot which seals the hole through the firewall. The boot itself has a protective soft rubber flap over the top of the main wire harness bundle. You can lift the flap up- it may be taped down, mine was- just lift the rubber flapper up out of way and you can see the harness go through the boot and can see exactly where it makes sense to cut. Tough to reach though.

Best of luck,

Mike
 

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2018 Lifted 6-speed Crosstrek
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I ran mine the same as Mike.

In the pic below, it shows the gas pedal bolted to the firewall. The wire on the right (multi-colored with a sheath) runs from my switch panel up the firewall and through the boot with the main harness.

299817


Had to deep dive in my build journal to find that pic lol. From October 2017.
 

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Discussion Starter #6
@stupidchicken03 Thanks for finding that photo. I felt much more comfortable making the cut after seeing that pic. I was still worried about cutting wires, but after I made the hole I realized the wires were in their own protective casing on top of being protected by the tube which would have made accidentally cutting those wires pretty unlikely. Successfully passed a coat hanger through!
 

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'18 and '19 Crosstrek Limiteds
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LOL, my "fishtape" is a reel of garden wire. Works really well! 😸
 
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