I have a Ford Fiesta TDCi 2013 my heated windscreens are very temperamental. One day both will work and then the next they will not, I took it in to Ford and they checked the electrics and rang me to say it was OK. I picked it up and they did not work ! the day after they worked fine all day and the next morning but then the afternoon they failed ? How can this happen can anyone suggest anything please ....