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Adding Wire Through Firewall

Discussion in 'Gen 4 Prius Accessories and Modifications' started by impr3, Feb 13, 2021.

  1. impr3

    impr3 New Member

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    I am looking to bring a 6ga wire from the engine compartment through the firewall into the cab of my 2016 Prius. I've been reading around online and the most promising thread is here:
    Getting wires through the firewall | PriusChat
    However, sadly the link to the instructions is dead... I'm trying to follow the hood release cable without the instructions and having difficulty finding it again on the other side of the firewall. Can someone point me toward the details of either this method or another approach to getting wires through the firewall? Thanks!
     
  2. Elektroingenieur

    Elektroingenieur Senior Member

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    The thread you’ve linked is about Prius c, a different model. The Electrical Wiring Diagram (more info) has a Location & Routing section with illustrations that show where the existing wire harnesses pass through the firewall; see my previous posting for more about this.
     
  3. impr3

    impr3 New Member

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    Thank you for your link. I followed another link in that thread and found these relatively detailed instructions: Power through the Firewall (Gen 4) | PriusChat. This approach worked very well though there were a few hiccups along the way. To help out others who are trying to do the same thing, I've taken a few pictures to illustrate the directions, particularly the spots where I had issues.

    I'm not sure how to quote between threads so want to give due credit here. The following instructions in "quotation marks" are from William Redoubt in the thread linked above. I have added my own comments without the quotation marks as well as pictures from throughout the process.

    "1. Remove the rocker panel trim by pulling it off (has clips only)."
    20210214_184351.jpg

    "2. Remove the kick panel by removing 1 plastic nut (fingers only -- it's not tight) near the brake pedal and pulling on it."
    20210214_184408.jpg

    "3. Remove "modesty panel" by removing two phillips-style screws and fiddling with a single tab under the steering wheel."
    Not sure if what I removed is the modesty panel, but it did come out with two Phillips-style screws and gave me a little move visibility.
    I didn't get a picture of this but the description above is pretty clear, it's the small panel above your feet when you're sitting in the driver's seat.

    "4. Lay on your back over the rocker panel and look above and to the left of the throttle linkage. There will be a large encased wire bundle running through the firewall at an angle running from left to right. The grommet is quite a bit larger than the encasement of the wire bundle and the encasement provides lots of protection for the wire bundle itself."
    The picture in the step below gives a good visual of where the boot is. I didn't take a picture before inserting the wire.

    "5. I pierced the grommet on the left side, pressing the screw driver through at an angle pointed toward the location of the battery, and then used a standard electrician's fish tape to get into the engine bay. I then pulled a "pull string" (a pretty stout piece of nylon braided cord) into the cab."
    Sadly I do not own an electrician's fish tape so I used a straightened out coat hanger in place of the screwdriver and connected my wire directly to it with a great deal of duct tape. I recommend entering on the left as described in the original instructions, starting by piercing through the lower left of the bundle and then aiming up at about a 45 degree angle without any angulation to the left or right. You'll feel your coat hanger slip past the bundle and then pop through on the other side. By having such a sharp angle, you avoid just following the path of the existing wire bundle which makes it hard to pop out of the boot on the other side...
    20210214_184510.jpg
    If, like me, your coat hanger breaks in half when you unbend the middle and you then have to hook two sections together, you MUST wrap the hooked together section in duct tape as well. While most of the wires are inside the encasement as described in the original instructions, there is at least one loose wire which will easily catch on any hooked ends and cause major problems... I ended up shorting out a minor circuit by pulling hard enough that the end of one hook pierced the insulation of a wire (the rear cigarette lighter circuit). Wrap the bloody thing up well so you can avoid making the same mistake as me!
    20210214_185228.jpg

    "6. I attached the wire the the pull string and pulled it through. I used 2 strands of #12 braided wire from Lowes. 25 feet is sufficient. Make sure you "streamline" the attachment to the pull string to make the bundle as small as possible. You can also use a bit of lube to make it slip through easier."
    As described above, I emitted several steps and just connected my coat hanger directly to my wire. In the picture you'll notice that the duct tape is built up to produce a slow taper in size up to my 6ga wire. In fact, the widest point is before the wire so that the boot gets stretched out before catching on the wire itself (meaning less force is applied to the wire and thus less risk of separation from the coat hanger). Since my wire has a relatively rubbery surface, I actually wrapped a long section of it in duct tape (applied length-wise) to smooth the surface out instead of using lube (which is electrically conductive). The picture below was taken before the extra wrapping.
    20210214_185317.jpg

    "7. Pull the wire through. That's it! Very simple. The biggest challenge is to get the fish tape through the mess of pipes and tubes between the engine and firewall. For me a couple of twists and push/pull and it popped right out into the clear."
    It's a little tough to see the boot from the engine side but you can see the wire coming through. I found that pulling the wire through involved enough force to dislodge the boot itself toward the engine side of the firewall so I had to give the wire bundle a good tug back toward the driver's foot well at the end to get it back into place.
    20210215_132343.jpg 20210215_133031.jpg
    I strongly recommend a set of long handled pliers like the ones pictured as this was the only way that I was able to reach the wire to pull it through...
    20210214_185554.jpg
     
    RicardoBR likes this.
  4. thomassster

    thomassster Member

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    coming from inside and pushing the wire out to engine side is my preferred path. When I did it, there was much more room above the harness instead of below. I like a bit of neatness with my wire and to make things less stressful, I went about removing the wiper cowl for better clearance. This will relieve any difficulty with the long pliers. If you DIY your car often, learning to remove the wiper cowl is good thing to learn to do. It takes me 15 minutes to remove with my impact driver and tools.