Thanks Peter,
At the moment it is working with the spare key so I will keep an eye on it. I have had that board off a few times - in my case (related to the heater fan and the speedo) it was down to the flyback diodes being under specced (Dan at Krazy Horse found that for me) - those are replaced on the board that is in the car now, and I have just done the same on my spare board.
So I'll leave it for now, then dash off and test connections if it comes back. Then swap to my spare board of that doesn't fix it.
Nick
