When testing with the compass hold it about 4 inches below the center of the axle. That is where the magnet is and will give you the best test.
If all three wheel on the curb side fail this test you are looking for a broken wire as it crosses from the drivers side to the passenger side. If one or 2 fail look at the wires from the frame to the backer plate of the brake. Sometimes they are routed poorly and pull apart due to axle movement. I like to leave a service loop at the frame end of these wires and secure them to the spindle with tie wraps just before they go into the backer plate. The movement is at the axle end thus the service loop.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles