To install electric trailer brakes, first remove the existing hub. To remove the wheel, uplift the trailer and support it. Gently pull out the grease dust cap using a screwdriver. Beneath the cap there is a large nut or a cotter pin, and above the nut there is a small metal clip.
Use a screwdriver to remove the small metal clip or straighten the cotter pin and remove it. It comes right off. Behind the nut there is a washer. Be sure to prevent it from falling down as you pull the nut out. Pull the entire hub carefully out from the axle.
Identify the correct backing plate, which is normally marked "right" or "left." Carefully insert the washers under the nut and secure them firmly. Take note of the two green wires, one of which should be tucked inside the black plate. Then connect either wire to the brake magnet, as there is no wire that is grounded.
Confirm that the outer bearing is greased before putting in the hub, the washer and the nut in that order. Thread the nut and turn the hub approximately 40 feet-pounds to firmly seat the bearing and the hub. Stop turning the drum once the nut is firmly secured and carefully loosen the nut until it is finger-tight. Prevent the nut from spinning off by inserting the copper pin. This ensures the tire remains intact.