You just picked up your new trailer and the brakes won't engage! Don't freak out, this is a common misconception. Trailer brakes need to be broken in. Don't load your trailer until you are sure your trailer brakes are fully engaging.
Electric drum brakes will require a break-in period to achieve full performance. This break-in period applies for new axles and any time new brake shoes and/or magnets are installed as part of regular maintenance. The break-in period for most drum brakes can range from 20 to 50 brake applications.
To break in your trailer brakes, the brakes can be seated in by applying approximately 8-10 volts to the trailer brakes at an initial speed of 40 mph and allowing the truck/trailer combination to slow down to 20 or 25 mph. For best results do not use truck brakes during this procedure. The trailer brakes will seat in faster by using them to stop both the truck and trailer. The easiest method is to apply the trailer brakes using the manual activation lever located on the in-cab brake controller.