Help trailer brakes went out (UPDATE)

I have had this same problem twice on an older Alumascape. Both times it was a problem with a broken or worn wire at the wheel. The first time the wire had rubbed against the wheel until the insulation was gone, then it would short out every time it touched a ground. The solution was to replace the wire and be sure it and all the other brake wires were wire-tied away from the wheels. The second time one of the butt connectors corroded and broke. This was discovered after symptoms like your described - first intermittent, the complete failure. New connectors took care of that problem. Good luck on your troubleshooting!
Carroll