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The installation instructions on both seem pretty straightforward, but the trailer brake controller comes with a wiring harness that plugs into a factory plug under the dash. This plug is gray in color, has 4 pins, and it located directly behind my OBD-II port. Every thing I can find on YouTube, forums, and even Curt's website say "just plug the brake controller in with the included adapter and bam! Trailer brakes!". This makes no sense to me as the 7 way plug will still need a 12v wire coming from the battery of the truck, and a wire from the brake controller, ran back to it.
If I have to cut the plug off of the brake controller and manually wire everything in per the instructions on the 7 way conversion kit, I'm alright with that, but then why include a fancy harness?
My main questions are: What is this gray, 4 pin plug? What is it's function? Where do the wires from this plug go? How does plugging the brake controller into it do anything?
Thank you in advance for any assistance yall are able to offer & apologies if I'm just being dumb. Gray plug location. Passenger side of steering column. Inside of gray plug
C136 under the frame somewhere will have the blue brake wire and another wire for trailer battery power. You will have to find this connector to get trailer brakes to your new connector. I would go to Pick an Pull and remove C136. Otherwise you have to splice into the blue wire.
I don't have an F150 but my Econoline van has the same trailer wiring setup
Sorry, doing all this on my phone and the small screen is causing me problems.
Connector C411 seems to have the trailer brake and trailer power wires. I can't easily identify all the other wires on C411 but here it is. Pin 9 dark blue is the brake signal.
I spliced into the harness & everything seemed to be functioning correctly, but when I hit the brakes, there is about 7 volts sent to the blue wire which the trailer brake controller does not like & throw an error message stating it is overloaded & there is a short to power somewhere. The controller will also randomly show "trailer connected/disconnected" when hooked up and with the truck running, regardless of pressing the brakes. Did you run into this issue with yours?
*edit* I measured the 7 volts when pressing the brake with the trailer brake controller disconnected from the harness while the truck was running. Just checking the blue wire at the connector under the dash, and the brake controller pin on the 7-way in the rear. The other pins on the connector under the dash were ground, battery power for the controller (14.5 with truck running) & the brake switch signal (around 12v with the truck running).
Last edited by CalhounMoto; Mar 18, 2025 at 10:46 AM.
I don't have any experience with your model year and brake controller. You may have to change a setting in the ECU (or other module) to get the controller working with the rest of the system. But nothing in the wiring diagrams suggest this.
The trailer brakes should come on slowly and peak at a voltage based on the gain setting. You can test this with a 12v light.
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