Wire through firewall - 2016

[dicko]

I am in the process of readying my 2016 C-Max SEL for towing behind my RV.  I am adding a Roadmaster Brakemaster supplemental braking system as well as a switch to the brake pedal and running-, turn- and stop-lights operated from the RV.   This requires six wires and an air hose to pass through the firewall.

 

After searching for what seemed like forever I found two ready-made holes sealed with plastic covers in the vertical portion of the driver's firewall.

 

Just to the left of the grommet through which the steering column passes you'll find a threaded stud which is used to secure the carpeting.  Pull back the carpeting and slit the felt carpet pad with a razor just to the left of the stud.  Make the slit vertical, four or five inches long, so you can get your hand behind it.

 

Put your hand behind the felt, about an inch to the left of the stud and feel your way up about three inches.  You should encounter a rubber cap inserted into a 3/4" hole through the firewall.  Use this hole if you wish but understand that there are things in the way on the engine side and fishing a wire is difficult.

 

The second hole is about three inches above the first one and maybe an inch or two to the left.  This one is like a Christmas present because it measures 2.5" x 3.25" and is a straight shot into the engine compartment with nothing in the way.

 

Even though you can't see up there unless you're a small person, the cover is easily pried off with your fingers.

 

I drilled a 1/2" hole in the cover for my wires to pass through.  I was originally going to use flexible wire loom to protect the wires on the engine side until I noticed that, with the aid of a flashlight, I could see the hole from the engine side.

 

I stuck a 1/2" Pex plastic pipe from the front of the engine compartment down through the big hole in the firewall and inserted it into the hole I had drilled in the plastic cover.  I then replaced the cover in the firewall and secured the other end of the pipe with plastic wire ties to make a rigid structure.  This provided me with a protected wire chase from the passenger compartment to the front of the engine compartment next to the electrical center.

 

The first picture shows the big hole cover with a small piece of Pex tubing inserted into it as a test.  The second picture shows the engine end of the Pex pipe after I had threaded the wires and air line through it.

 

     -Dick-

 

 

 

 

[RobMax]

Nice job. Interesting choice of towed vehicle. Trying to make up for the low mileage on the RV?  :)

[ScubaDadMiami]

When I had my cell phone and charging cable installed, I observed the installer going through the fire wall by following right up the middle from the console, and then he fished the cable through the middle of the firewall, pretty much at dead center.

[dicko]

Nice job. Interesting choice of towed vehicle. Trying to make up for the low mileage on the RV?  :)

Actually it's our daily driver that replaces a 2007 Prius.  Our other vehicle is a Ram 1500 into which we load my Harley to take on trips but the truck is a pain in cities with heavy traffic so if we don't take the bike we will take the C-Max.  Clever?

     -Dick-

[jdbob]

Thanks dicko the information. I just used that firewall opening to run a wire from the Park switch on the shifter to my DIY LED daytime running lights so they wouldn't come on when in park. Got tired of having them running for hours and hours while charging my 2013 Energi.

[Joe P]

Thanks for the info Dick. I'm doing the same thing and this is a great help. Happy towing.

[BobRay]

@dicko  How did you route the tail light wires through the car? 

 

BTW, thanks a million for the tip on getting the wires through the firewall! :) That's a great solution.

 

For others, you can see where the wires come out if you look below the brake fluid reservoir (easier if you take out the screws and drop the reservoir to the left). Look for the round aluminum thing way back at the firewall. Just below it, you'll see a rectangular black (at least on mine) felt cover about 2" x 3" with an indentation in the center. That cover stays in place when you remove the grommet, but if you push on the bottom of it from the inside, it will tilt up leaving a hole below it.

 

First, you have to get through the soundproofing crap. It's easy enough to rip a hole with your fingers to feel around for the grommet (as dicko says, a few inches to the left of the plastic grommet that holds the sheet of rubber and about 6 inches up). It has square corners. That's not enough to remove the grommet, though. I'm big enough that I couldn't get two hands up there to use a knife. I ended up snipping at it for about an hour with a sharp pair of heavy duty scissors while sitting on a 6" high box outside the door. The stuff it maddening. Every time you open the hole, it closes back up on its own just to spite you. Once you've opened the hole enough to remove the grommet, grab the upper left corner and pull it to the right and inward. The grommet will pop out.

 

Now if I can just figure out how to get the tail-light wires to the back end without them showing. The e-trailer videos all show the wires running under the car, which is pretty much impossible without a lift.

Edited September 5, 2019 by BobRay