The humming means that you have power to the brakes but that is just the first step of actuating electric brakes. The power activates the electric magnet which pulls itself onto the inside face of the brake drum and causes drag. The electric magnet is mounted on a lever that forces the shoes into contact with the drums when the magnet has drag on it. The magnet needs good contact with the drum face to work properly, the lever needs to work freely and have enough travel to activate the shoes and the shoes need to have pad left and be adjusted properly. The drums need to be grease free. All of this needs to be inspected for wear and free movement. If you pack your brakes using a grease fitting on the end of the axle be aware that if the grease seal on the axle leaks you are also greasing the brake shoes which makes them not work. Based on my experience I would take the bearings out and grease them by hand. I have become very disenchanted with electric drum brakes in the past couple of years due to constant issues with them. I recently upgraded to electric over hydraulic. It was expensive but now my brakes work effectively and consistently. I feel that it was a good investment in my life expectancy.
