I have tested it in the dark and there doesn't seem to be any difference when you shine the light. I shined a torch right at the mirror and it practically blinds me in the driver seat so I am pretty sure this isn't working at all. I guess it's a case of next steps now. Check the fuse? I will try to dig out the fuse diagram and see if I can see which one it is. Is there any way to check the connector at the back of the mirror to verify that there is a supply to the mirror?