u will be able to feel theheat off the windscreen if its working or not...put your palm over the edge of the glass then move slowly across till ur hand is over the heater lines...take off the scuttle panel and check the connection (centre of the glass) and then check the earth inside the interior light.. we get them in work all the time with this problem..altho its normally the earlier focus that has this problem as they have 2 seperate connections for each side of the screen. i have done a few at work tho where the heater lines seem to just stop working..various reasons for this