Troubleshooting Brake Output Circuit that has Voltage all the Time  

Question:

Expert Reply:

The brake output circuit of your 2008 Toyota Tundra should not have 12 volts without the brake pedal pressed or the manual override of the controller slide. This would indicate that either the brake controller is bad or you have a short on your trailer connector wiring.

I would first check the back of the connector for corrosion or exposed wire and fix as necessary. The 12 volt accessory circuit may be shorting out to the brake output circuit. If that doesn't fix the problem you will need to turn your attention to the controller.

Testing the brake controller is fairly easy. Sever the blue brake output wire near the brake controller leaving enough room to reconnect it and then apply the manual slide. Using a circuit tester like part # PTW2993, you should get output to the controller side of the wire you severed. If the manual slide activates the trailer brake output wire properly, try the brake pedal. If the brake pedal activates the brake output properly also then the problem is farther back either in the vehicle wiring or on the trailer.

If either the brake pedal or the manual slide are not functioning properly you will need to test the wires going into the brake controller. Make sure you have power entering the brake controller on the black wire. On the red wire you will only want power when the brake pedal is pressed.

If there is power on the red wire before the brake pedal is pressed you have connected the red wire from the brake controller to the wrong circuit. You would then need to find the brake switch wire that has power ONLY when the brake pedal is activated.

If these connections check out and the brake controller is properly grounded then there is possibly a problem inside the brake controller.

I am including a link to a video that will show you how to test the wiring on a brake controller.

expert reply by: Jameson C

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