OK to update and clear up the mystery of the missing thread. Searching the internet I realised what I thought was a thread on here was in fact a video on YouTube. A guy in America shows how he did it. He took the seat out and did it in the comfort of his garage. It looks a pig of a job with so many parts to remove or disconnect. I'm not sure want heated seats that much, maybe if I get really bored when the weather improves !