Lacking the instruction sheet, try this:
Hook up your trailer, "reset" the actuator - usually in the rearward position.
Try to pull forward. If resistance from the trailer then the brakes are engaged.
If resistance then try the opposite reset position and repeat the trailer pull.
The whole idea of the "breakaway" cable is to set the brakes on the trailer if the ball & coupler become separated.
P.S. If you have a 5 or more wire trailer wiring harness, then you need to plug in the car to trailer harness
as one of the wires electrically disengage the brakes when backing up or down a grade.
Actually any backing motion would lock brakes if the harness is not connected.
Captain Tony
2005 Summit by Triton - 220T Platinum 3Log
2005 115HP Mercury Optimax - 228 Marine Master Trailer
St. Louis & Lake of the Ozarks, MO.