hi phil,,,,,,,,the problem with the 260 model that it suffers with wires breaking either in the looms ,between the top skate and bottom cluster assy behind the carriage or actualy in the top skate or bottom cluster[aspecialy on bends of the rail],,,,,,,it sounds to me that yours is a directional fault where a wire is intermediatly breaking as its going round the bend, in your case remove the top skate cover and pull on the wiring on the upside safety edge switches to see if one is breaking if ok check other upside safety edge wiring............hope this will help,,let me know..
paul...portsmouth/uk
PAUL
April 2013