There is no direct connection between the hrw switch and the rear glass. This function is controlled by the body electric module. I would check the fuses first. There is a fuse box in the roof of the glovebox,(access is a bit tricky), there is also a fuse box next to the battery( a real pain to access.) Does this car have heated door mirrors,and if so,do they work? Could also be a broken wire up to the tailgate, from the body. Do other functions in the tailgate work? rear wiper ?

Not sure if it's got heated mirrors. If it has then they didn't clear this morning! Tailgate, wipers etc all work. Is the body electric module replaceable? Would there be a relay or fuse in the box under the bonnet I can check. The one in the glove box is ok. Thanks

The relay is integrated into the engine bay fuse box.It is not a replacement item without the whole unit. There are fuses in the engine bay fusebox, but access is very difficult. You may have to remove the battery to get the lid off

Thank you for your help. I'll have a look tomorrow and try and trace the cable to see there's a break in it. I dis notice the cable to the high level brake light has been repaired so will start in that area Will also check to see if mirrors are heated as well.