Gordon Bennet, if it IS the switch it's unfit for purpose, its barely been used.
They told me that they "suspected" the switch was faulty after charging me £84 for a "diagnostic". It was just the same as the OP's fault: sometimes worked perfectly but mostly wouldn't work at all. I got my £84 back after I traded the car in for a new one elsewhere! The Fiesta Mk7 is a fantastic car but that experience put me right off it.
Haynes don't usually produce workshop manuals for any car until they reach a certain age and sufficiently high numbers have been sold. My best guess is that there will soon be a revision of the Mk7 manual to include the 2014 facelift version as there will undoubtably be a sufficient market for it!