I had a box trailer with dual axles and disk brakes on each axle. It was really a pain to back. Once while I was on a mountain in WY and had to jack knife the trailer and both axles brakes were locked. I took a flat bar about 5/16 inch thick and bent to to fit in the box between the tongue of the actuator and the trailer box (it would go behind those bouts you see in the photo of U see correctly). It stops the actuator from pushing on the master cylinder. Some as yours does not have a electrical connection between the reverse lights and a solenoid valve.