Primus IQ Trailer Brake Controller Does not Go Higher than 4.0 When Set to Maximum Output  

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Expert Reply:

With the Primus IQ trailer brake controller # TK90160 you can adjust the power output. If yours is not going higher than 4 volts output when set to the maximum then there is some issue that we need to troubleshoot. First, make sure the controller is mounted within the parameters outlined in the instructions (linked for reference) and that it is not turned or tilted to the side. Proportional brake controllers can behave erratically when mounted off kilter.

Next, you can test the controller using a multimeter such as # PT89ZR. Sever the blue wire a few inches back from the controller and test the end coming out of the controller. Fully apply the manual override while testing the wire. It should show at least 12 volts if set to the maximum. If it shows much less or shows power without the manual override pressed then there is a problem with the controller and it will need to be replaced.

If the controller checks out fine then the issue is most likely related to the wiring. After reconnecting the blue wire you will need to trace it from the controller to the trailer connector looking for breaks in the wiring and fixing as needed. Also make sure the vehicle and trailer side connectors are clean and corrosion free inside and out and properly grounded.

Also inspect the brake magnet wiring and make sure the grounds are attached to clean and corrosion free bare metal surfaces. Visually inspect the magnets and if you can see the copper windings coming through they will need to be replaced. To further test the magnets you can follow the how-to article I have linked.

I have included some links on testing and troubleshooting brake controllers for you to view.

expert reply by: Michael H

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