Drivers rear side light

  1. #1
    Took my car for MOT earlier this week and one of the things it failed on was drivers rear side light. Changed the bulb and cleaned all the connections thinking that this was the problem but it still would not light up even though brake light comes on. Changed the whole unit and cleaned connections still no joy. A friend of mine wired the unit direct to the battery and it unit lit up. Any ideas what could be causing this?