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Troubleshooting Brake Controller Installations

Even the most experienced installer will encounter it from time to time: the brake controller installation is finished, the wires have all been run, but something is going wrong. Whether your controller is showing an error message or the trailer brakes just aren't working, there are a number of troubleshooting techniques you can use to get the problem fixed and get back on the road. Using the following information and testing procedures, you should be able to pinpoint and eliminate the most common issues encountered during and after a brake controller installation.






Common Brake Control Issues


ProblemPossible IssuesTesting Procedures
Brake controller display does not show that trailer is connected.
  1. Short on brake signal wire, trailer or vehicle side.
  2. Corrosion in trailer and/or vehicle plug.
  3. Short on brake magnets on trailer.
  4. Malfunctioning brake magnet(s).
Brake controller loses connection to battery ground.
  1. Ground wire was not connected to negative battery terminal, ground area does not have solid connection to ground.
  2. Adapter wiring does not match OEM connector on vehicle.
  3. Ground connection to negative battery terminal is loose.
  4. Ground wire has been damaged and exposed wiring is touching a metal area.
Brakes are applying too aggressively for the brake controller settings.
  1. Brake assemblies are not properly adjusted.
  2. Boost/Gain on brake controller is set too high for trailer size.
  • Adjust brakes properly (see video).
  • See brake control owner's manual for proper boost/gain settings for trailer size.
Trailer brakes only work with manual control, not with brake pedal.
  1. Incorrect stoplight wire connection.
  2. Adapter wiring layout does not match OEM connector on vehicle.
Brake controller detects an overload condition during use.
  1. Trailer has too many brakes for brake controller to handle.
  2. Corrosion in trailer and/or vehicle plug.
  3. Brake signal wire on trailer is damaged, exposed wiring is touching metal area or another circuit.
  4. Malfunctioning brake magnet(s).
Display is erratic while braking.
  1. Short to battery on 12V wire connection.
  2. Short on brake signal wire, trailer or vehicle side
  3. Corrosion in trailer and/or vehicle plug.
  4. 12V wire was not connected to vehicle battery, 12V source used is not constant.
Brake controller detects a short on the brake wire while vehicle is idling.
  1. Corrosion in trailer and/or vehicle plug.
  2. Brake signal wire on trailer or vehicle is damaged, exposed wiring is touching metal area.
Trailer brakes engage when it is plugged into the vehicle.
  1. Incorrect stoplight wire connection.
  2. Corrosion in trailer and/or vehicle plug.
  3. Adapter wiring does not match OEM connector on vehicle.
Brake controller does not turn on.
  1. Connection to battery is not complete.
  2. Vehicle is missing a fuse or relay required to power 12V power circuit.
  3. Adapter wiring layout does not match OEM connector on vehicle.
  • Method 1
  • Check fuse block for missing fuse/relay. See vehicle-specific FAQ if available, or check owner's manual.




Basic Testing Procedures


Method 1: Verifying Correct Wire Connections (Hard Wire Installs)

Testing the Stoplight WireBrake Control Wire Colors
  • Make sure that each wire is connected in the correct location. Standard wire colors are listed, but check connections by function if colors vary.

  • Verify that the white brake controller wire (ground function) is connected to the negative battery terminal.

  • Verify that the black brake controller wire (12V power function) is connected to the positive battery terminal with a 20 or 30 amp circuit breaker installed in line. For trailers with 2-4 brakes, use a 20 amp breaker and for trailers with 6-8 brakes, use a 30 amp breaker.

  • Use a 12V probe-style circuit tester to verify the stoplight wire (red) connection (Figure 1). The tester should show power when the brake pedal is pressed, and should not show power when the pedal is released.

  • If all connections are correct, proceed to Method 2.





Wiring Adapter vs. OEM Connector

Method 1: Verifying Correct Wire Connections (Plug-in Installs)

  • Use a 12V probe-style circuit tester to verify that power is present at OEM connector. You should be able to get a solid power reading on one pin/slot, a reading on a second pin/slot only when the brake pedal is pressed, and at least two other pins with no power present.

  • Verify that the pin/slot layout of the wiring adapter you are using matches the layout in the OEM connector. The two plugs should be mirror images.

  • Check the part number on the adapter and make sure it is the same as the listed fit for your vehicle.

  • If all connections are correct, proceed to Method 2.





Method 2: Testing for the Brake Signal

Testing the Blue Wire
  • Use a 12V probe-style circuit tester to verify that power is present on the blue wire behind the brake controller when you use the manual control (Figure 2). If no power is present, the brake controller may be malfunctioning and require replacement. See video for reference.

  • Without the trailer plugged in, use a circuit tester to verify that power is present at the vehicle 7-Way when the brake pedal is pressed or the manual control is used. The electric brake pin should be in the 5 o'clock position. If no power is present, proceed to Method 3.

  • With the trailer connected, check for power on the electric brake wire coming out of the trailer's 7-Way plug. You can repeat the test on this wire, moving further back toward the magnets each time. If power stops, look for a short or ground issue (Method 3).





Method 3: Looking for a Short or Ground Issue

Damaged Wiring
  • If controller was hard wired, verify that the white ground wire is attached to the negative battery terminal on the vehicle.

  • Check along any wiring that was run from front to back on the vehicle and look for spots that have been nicked, pinched, or rubbed and have copper wire showing through the jacketing. Wrap any damaged areas with electrical tape.

  • Inspect the trailer wiring that runs from the trailer plug, again looking for any damaged spots (Figure 3). Wrap any damaged areas with electrical tape or replace the wire section, if the damage is great enough.

  • Look inside the front and back sides of the vehicle and trailer plugs to determine if any white or green corrosion has accumulated over time. If you see any corrosion, you will need to either thoroughly clean the plug or replace it. A wire brush works best for cleaning.

  • Check the wires on the trailer brake magnets. Each magnet should have two wires: one for power, and one for ground. Make sure that the ground wire is attached to a clean metal area without any paint or corrosion. The power wire should be intact and have a solid connection to the electric brake signal wire. It does not matter which wire does what, just that one wire is powered and the other is grounded.





Method 4: Inspecting the Brake Assemblies

Brake Magnets





For more information, see:

  • Vehicle-specific FAQ articles, if available.






















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