How to Test a Brake Controller to See if it is Putting Out the Correct Voltage  

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There are several ways to test a brake controller. Since you want to check for voltage you would need a multi-meter, # PT89ZR, if you do not already have one. First, you need to test the voltage at the controller. Set the controller to maximum output. Then sever the blue wire several inches from the back of the controller. Set the meter to test for voltage. Test the end of the blue wire coming out of the controller while fully applying the manual override.

You should be getting around 12 volts if not slightly more. If you get less voltage at the controller then that indicates an issue inside the controller and it should be replaced.

Next, reconnect the blue wire at the back of the controller. You can then test the voltage output at the vehicle side trailer connector. Again you will be testing the brake output circuit (pin in 5 oclock position). Have someone sit in the vehicle and fully apply the manual override. You should be getting around 12 volts again (a slight drop of a volt or so is expected). If you get less then there is some issue between the connector and controller. It is most likely a loose or broken connection.

Next you can test the output on the trailer side. Plug the trailer in to the vehicle and test the brake output wire behind the trailer side connector and at the magnets. Any drop in voltage indicates a wiring issue that needs to be addressed. Make sure the main trailer connector ground and the magnet 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 using the meter I have included a link to a help article that explains what to do and what to look for.

expert reply by: Michael H

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