Installing a Hardwired Electric Brake Controller With No Available Engine Firewall Wiring Passage

Dbremmer

To summarize a possible solution, follow the path of your hood release cable from lower dashboard or side wall to where it activates the hood latch.  You may be able to use this same channel to feed wires into the engine compartment.  This approach may work for several car models that do not offer good firewall wire pass through access.

My TV is a 2012 Toyota Highlander Hybrid.  A  few years ago I went to a U-Haul center to have a brake controller installed before purchasing a new T@B 320.  The technician assigned to the job declared the installation impossible on my car because there is no clear access through the firewall into the engine compartment.   They sold me the Curt Echo wireless bluetooth brake controller.  I did not like the clumsy attachment of the long cylindrical controller in my 7-way trailer wiring socket.  It did work OK for 2-years, then on a recent road trip from southern California to Seattle Washington, coming back through the Oregon coast and the California Redwoods, the unit fell into an extreme operation mode, locking the trailer brakes no matter how gently the brakes are applied.  I tried several setting adjustment combinations,  sensitivity and max output  all the way down to 10% output, and lowest sensitivity.  These setting changes made no difference to the unacceptable and dangerous trailer brake lock up behavior.   In San Francisco, I pulled over and removed the Curt Echo from my trailer connection and drove the rest of the way home with just TV brakes.  Fortunately the T@B 320 is light weight.  

The real scandal is that with a factory installed tow package, many automobile manufacturers provide an isolated circuit wire harness that serves just trailer lights.  Highway safety regulations require brakes on trailers over a given weight limit.  Tow packages should include a harness and connector convenient under the dashboard to enable hookup of an electric brake controller.  I suspect that this desired complete tow package wiring is available more often in trucks than in sedans or SUVs.

I searched and probed under my dashboard  finally understanding why the U-Haul technician  gave up.  Previously when replacing spark plugs on that TV, I followed the procedure for removing windshield wipers and a tray structure underneath, gaining access to the back engine side.  If I found or created access somewhere there, it would be high up behind the dashboard.  Unknown obstacles make this approach problematic.  There must be an easier path not requiring so much disassembly and working around obstacles.  

I noticed the region above the driver side front tire.  The surface above the tire has a fiberboard material splash guard cover that is easily removed once the wheel is taken off, by taking out some fender bolts and plastic push in fasteners.  That splash guard creates a channel from approximately the side wall at the base of the dashboard to the wheel metal wall along the side of the engine compartment.  Knowing this, I did a Google search with terms suggesting the passing of wire from the interior to the engine side wall compartment.  Sure enough in a Toyota owners forum,  a Highlander Hybrid owner described how he passed wires through the side wall grommet and along the path of the hood release cable.  The cable passes through that channel between the fiberboard  tire splash guard and upper fender wall.  Using a stiff wire such as a coat hanger wire you can poke it into the “tunnel” where the hood release cable travels and exits into the engine compartment at a convenient location below the main fuze box.  Taping hook up wires to that stiff wire you pull them through for connections in the engine compartment.  In the Hylander Hybrid, the 12V battery is in a rear interior compartment, but a high amp buss wire brings 12V to terminals in the fuse box. You can essentially make battery connections there.

This exploration gave me the confidence to purchase my hard wired brake controller.  I ordered from Etrailer.com a Redarc Tow-Pro Liberty.  The cable connection from the main body to a minimalist dash board control knob provides flexibility for a neat and clean install.  I used strips of 3M Scotch Mount double sided mounting tape to attach the main controller body to the bottom of a metal box up in the dash board near where that hood release cable passes through the wall.  I drilled my own wire pass hole with added rubber grommet in the side wall from the wheel well side about an inch away from  the hood release cable pass through.  I just did not want to disturb the hood release cable.  The final challenge was getting a 12V “brake applied” signal for the controller.  The wire connector for the brake pedal switch was up high in a crowded space very hard to work in.   I found it easier to run a wire from the output of the factory tow package harness, tapping into the green (brake light/ Right turn) wire and running underneath the floor board from trailer hitch up to the driver front wheel well and into my port in the side wall.  A possible consequence of using the combined brake/right turn signal is that simultaneous braking and right turn signaling might create a strange pulsating trailer braking.  This is an infrequent situation that may happen usually at lower speed.  I have tested this after completing the installation, calibration, and finding a best balance control setting (3 out of 0-10).  Braking while signaling a right turn, so far in testing,  does not create a noticeable problem.  I hope that sharing this experience will be useful to others.  A wired in brake controller is simple to use and reliable.

Horigan

The rubber gasket around the AC lines through the firewall are flexible enough to allow passage of additional wires.

SLJ

Typically a car with just a 4 pin for hook up to the lights is not rated to tow anything over 1,500 pounds. Might have been different back in 2012.

TourDeForth

Just a thought, you don’t have to run the wires through the firewall, you can enter the cabin some where from behind or under the seats and then run the wires forward under the carpeting and /or the door jamb covers.

Dbremmer

I looked at the AC lines during my original search.  This option looks good from inside the cabin, but the location is hard to access from outside.  The AC lines exit is not visible from above, but possibly visible from underneath.  One could try routing the wires up the firewall retrieving them from below and routing them up while avoiding exposure to exhaust heat.  I believe that the hood release channel that I chose is cleaner and actually easier to implement.  However, you are correct.  Where there is a will, there is a way.  I wonder why that U-Haul technician rejected the AC lines gasket option.  It appears to be the most obvious path.

As suggested, entering the cabin somewhere on the floor is also possible and requires properly covering wires up for some length.  Again, in this case I believe that using the sidewall and using the hood release cable as a built-in guide turns out to be the easiest to implement.  Consider that in all models with a manual hood release it should be possible to service and replace a failed cable.  This virtually insures a reasonable path to pass a stiff wire through.

I think that we all agree that good DIY trailer owners will indeed find a successful path to hard wire brake controllers.  This should encourage others who want controllers wired in by professional technicians that there must be good independent practitioners who will use some creativity to get it done right.

pthomas745

No matter what, this is really nice, creative work.

Horigan

Dbremmer said:

I looked at the AC lines during my original search.  This option looks good from inside the cabin, but the location is hard to access from outside.  The AC lines exit is not visible from above, but possibly visible from underneath...  

Interesting.  On my V6 Highlander they are visible and accessible from above.