Brake controller harness for 4th gen Tacoma?

[paranoiccritic]

Hi All,

I've followed this with great interest, and with lots of gratitude for everyone who's worked this out. I have a '24 TRD OR 4x4, base model with heated seats, Tow/Haul, DAC/CRAWL. I'm trying to find the best way to get to J7. I'm having trouble finding it under the steering wheel - is this where to find it? I do have the 6th pin in my trailer harness at the bumper/tailgate, and I'm trying to install a Tekonsha P3 near the driver's seat. My understanding is that I can run power from the battery, hit a local ground point, get the blue brake lead from J7 under the dash, and then tap into the brake light using a diode between the source and the Tekonsha. Just stuck trying to find J7, but I think I found the brake light wire to tap. I purchased 2 days of TIS, but these diagrams are a little cryptic to me. Any tips for finding J7 would be immensely helpful. Thanks in advance!

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[jharger]

For J7 I assume you mean the wire from the 7 pin plug that powers the brakes on your trailer. It runs from the plug to under the rear seat on the passenger side. (the heavy blue wire). You can run a wire along the harness that is beneath the trim at the door openings either on the left or right.

 

[paranoiccritic]

For J7 I assume you mean the wire from the 7 pin plug that powers the brakes on your trailer. It runs from the plug to under the rear seat on the passenger side. (the heavy blue wire). You can run a wire along the harness that is beneath the trim at the door openings either on the left or right.

Thanks - this is what i did. The connection point you shared is SQ9, and what it connects to runs to a place behind the dash, and I was hoping to be able to tie in behind the dash and not have to run the brake wire as you described, but it turns out I don’t have that run. I did confirm the blue wire runs from the connector you showed to the trailer connection, so we’re all good there. I’m still hunting for the brake light wire i’ll see the dash. I may just have to find it in the drivers side harness under the door trim. ::

 

[paranoiccritic]

Yea it seems no one knows yet all the wiring is missing.

I had to run all the wires myself and pay for wiring diagram. I still need to wire a diode as the truck doesn’t like power being applied to brake light circuit without brakes being applied.

quoting here way later than the above was originally posted, but can you clear the above error message (or a brake-related message) with the appropriate OBD scanner?

 

[paranoiccritic]

quoting here way later than the above was originally posted, but can you clear the above error message (or a brake-related message) with the appropriate OBD scanner?

the context is that I tried to probe the wires in the harness under the drivers side trim to confirm which wire goes to brake light. To do so, I tried to use a multi meter set to million volts, neg on the nearest ground point, and then finely scraping a tiny portion of insulation from the target wires (thinking this would be easy to patch if I hit a wire that wasn’t the one). The first wire didn’t generate any voltage when pressing the brake. the second wire, as soon as I touched the positive lead from the multi-meter, threw an error (“brake override malfunction”) and now the truck won’t start. hoping to clear this later with an OBD scanner

 

[ollie03031]

Not sure what the advantage is to a brake controller hardwired into the vehicle. I went to my dealer and they ripped the dash apart looking for a connector and they gave up and recommended the CURT 51180 Echo. I researched the echo and it does have some advantages and it’s low cost, but I did not like the idea of needing Location Services turned on, on my iPhone and the idea that the iPhone had to be running the app. That would take away my gps and music. I finally settled on the Tekonsha Prodigy RF wireless. it more expensive but does not use your iPhone, but uses a simple controller plugged into the aux power connector. All brake controllers have a two or three degrees of freedom toque sensor that senses when you slow down. It uses the knowledge that you are braking to enable the trailer brakes. The amount of slow down force detected by the torque sensor and the gain setting of the controller controls the amount of braking the controller applies. Either of these wireless controllers can be easily moved from one vehicle to another unlike a hard wired controller. There are probably many other wireless controllers that would work as well as those I listed.

 

[Sagebrush]

That would take away my gps and music.

Are you sure about that? Just because another app is running?

 

[paranoiccritic]

just to resolve the saga, in trying to probe, which wire was the brake light, I accidentally shorted out and blew the 10A STOP fuse under the dash. Replaced that baby unplugged the battery for a good while, and good to go. Was able to splice in a 15A/45V Schottky diode, wired up to my Tekonsha P3, and all is right in the world.

Call me old fashioned, but I’m wary of a wireless connection for something as vital as a brake controller. I understand the wireless connection is only for adjusting settings. Also, I had the controller, and aside from a few hours of anxiety over having possibly bricked my truck (before finding and replacing the 10A fuse), I had everything on-hand and it just took a couple hours.

 

[jharger]

I photo of where you found that brake signal wire might be helpful to others.

 

[jharger]

Thanks - this is what i did. The connection point you shared is SQ9, and what it connects to runs to a place behind the dash, and I was hoping to be able to tie in behind the dash and not have to run the brake wire as you described, but it turns out I don’t have that run. I did confirm the blue wire runs from the connector you showed to the trailer connection, so we’re all good there. I’m still hunting for the brake light wire i’ll see the dash. I may just have to find it in the drivers side harness under the door trim. ::

I think that Toyota used to use the same wiring harness for all trucks that included the plug for the brake controller. Either they wanted to discourage aftermarket controllers or the price of copper made it economical to have two separate harnesses for with and without the factory brake controller. Thus no wire from the SQ9 plug to under the dash. And some have reported no wire from the 7 pin plug to SQ9.

 

[paranoiccritic]

I photo of where you found that brake signal wire might be helpful to others.

good call - see here! the wire in question is blue, next to the red wire, with a small tag of electrical tape toward the bottom
of the image. This is under the driver’s door trim in a double cab TRD OR. If you are looking at the tacoma circuit diagram, this is the blue wire between AR2 and RG28. Folks installing the Redarc controllers seem to prefer the light green wire between R28 and gR3 under the back drivers side door trim. This makes sense, given that the Redarc control units are being installed under the back seat. The problem with tapping into this circuit under the driver’s door trim is that there are two blue wires. it may ultimately be a better choice to tap into the light green wire under the back drivers side door trim if there is only one light green wire there.

 

[paranoiccritic]

I think that Toyota used to use the same wiring harness for all trucks that included the plug for the brake controller. Either they wanted to discourage aftermarket controllers or the price of copper made it economical to have two separate harnesses for with and without the factory brake controller. Thus no wire from the SQ9 plug to under the dash. And some have reported no wire from the 7 pin plug to SQ9.

I had a pre-installed brake controller plug in my Gen 3 tacoma, and I did have the blue wire from SQ9 to 7-pin plug in my current Gen 4 TRD OR - not sure what the rhyme or reason is for this, but my new install was successfully tested last night C'est la vie.

 

[ollie03031]

Sagebrush, no I am not 100% sure because I did not try it myself. I just read a bunch of reviews. I know you can have multiple apps running at the same time on the iPhone. If you are using CarPlay and are displaying your gps route and you need the brake controllers app you have to switch apps before you can make a brake controller change. There was another issue with losing Bluetooth connection. That would be a problem if you needed to do a manual brake and lost connection. The Prodigy is not Bluetooth as I understand it but it is RF just a different frequency and modulatiand will work with up to three axils.

 

[Camperbunga]

Unfortunately, the manual says Toyota doesn't recommend the use of a third party trailer brake controller with this truck. That's quite frustrating, as other OEMs that offer factory-installed brake controllers also have provisions for aftermarket controllers.

Just bought a 2025 extcab, basically a two door Tacoma. I expected a brake controler and of course it does not have one. My 2016 tacoma had the socket and installation of a controller was easy. i accepted the truck even though it did not have a controller because everyone figured it would have the connector. Now after doing an internet search on 2025 Tacoma and brake controllers i find this web sight. I have my salesman and his service dept. looking into seeing if the stock Toyota controller can be installed but this site makes it sound close to hopeless. I am not quite ready to cut into cables yet but if nothing better comes up in the next couple months will pass the instructions listed previously to my dealer to have them do the install.
Ollie

first question I asked salesman. Does it have a plug for brake controller. He said of course. I should have made him show me. Now dealership says they can’t install one. They don’t know where the plug is because there isn’t one. Keep telling me they’ll get back to me. They simply lied. I have a curt wireless that worked fine on my old car. Can’t get it to connect to my 2025 Tacoma. The curt brakes continue to work even if you don’t have the Bluetooth connection. Prefer my takonsha controller but I’m at a loss. I can do some work on my truck but not wiring. Where do I find someone to wire a controller connection?

 

[Camperbunga]

Not sure what the advantage is to a brake controller hardwired into the vehicle. I went to my dealer and they ripped the dash apart looking for a connector and they gave up and recommended the CURT 51180 Echo. I researched the echo and it does have some advantages and it’s low cost, but I did not like the idea of needing Location Services turned on, on my iPhone and the idea that the iPhone had to be running the app. That would take away my gps and music. I finally settled on the Tekonsha Prodigy RF wireless. it more expensive but does not use your iPhone, but uses a simple controller plugged into the aux power connector. All brake controllers have a two or three degrees of freedom toque sensor that senses when you slow down. It uses the knowledge that you are braking to enable the trailer brakes. The amount of slow down force detected by the torque sensor and the gain setting of the controller controls the amount of braking the controller applies. Either of these wireless controllers can be easily moved from one vehicle to another unlike a hard wired controller. There are probably many other wireless controllers that would work as well as those I listed.

Omg thank you for this. I have the curt but it has issues. Going to look into this one

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