wheelock up

[dieselguy]

If you have your gain set high and are moving say under 15 mph ... they will tend to slide if there is some loose gravel on the pavement. A magnet will only try to grab the wheel drum if it's energized. I assume you saw nothing out of place as in the adjuster, cable, brake shoe mounting springs, small clip holding the magnet onto the lever arm. A short would probably pop a fuse or show a fault code on your brake controller. Could you more describe "lock-up"???