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Curt Triflex Trailer Brake Controller Shows Power All the Time on Blue Wire


Vehicle is a 2005 Nissan Pathfinder. When connecting trailer harness I am able to get all the lights to work, but no brakes. In troubleshooting, with a single dot on the display, I am seeing 12v on the blue wire coming out of the Curt controller without the brakes or manual activation slide activated. The voltage doesnt change when braking or sliding the slider. The controller stays in standby mode until either the brakes or slide are activated, so I dont think its a problem with the wiring. I get nothing but a single dot on the display when the trailer is connected. Should I be seeing 12v on the blue wire with a single dot and nothing activated?


Expert Reply:

You should only be seeing 12 volts on the blue wire on the brake controller, # C51140, when the manual override is used. If there is constant power all the time then there is either something that is miswired or a problem inside the controller and it will need to be replaced.

Brake controllers do send back a minimum amount of voltage to check for a connected trailer but it should not be enough to activate the brakes.

In the truck cab you will need to sever the blue wire several inches from the back of the controller. Then use your tester to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override. If it shows power at idle then there is something wrong with the controller and it will need to be replaced.

If it tests fine then reconnect the blue wire. Then move on to the truck side trailer connector. Many times, dirt or corrosion can cause a short in a trailer connector. Make sure the truck and the trailer side connectors are clean and free of corrosion inside and out.

You can test the brake output pin and it should only show power with the manual override. If it shows power any other time then there is a short somewhere between the connector and the brake controller you will need to track down.

If the truck side checks out fine then it could be the wiring to the brake magnets or the magnets themselves. Inspect the power wires to the magnets and look for pinched, frayed, or damaged wires and fix as needed. Make sure the ground wires are attached to clean and corrosion free bare metal surfaces.

You can visually inspect the magnets and if you can see the copper windings coming through the magnets will need to be replaced. To further test the magnets you can follow the help article I have linked. I have also included some help articles on testing and troubleshooting brake controllers for you.

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