Dropped a new deck and replaced the light switch in the el over the weekend, now my heater control will only run demist. Is this a common problem and if it is what have I unknowingly disconnected? I did not completely remove the facia when I did the light switch but poped out the cluster side enought once the screws were undone to get to the plug. I also could not be stuffed pulling the deck out once I had it mounted properly so I reached behind and plugged the deck in. Thats all Ive done and it was working prior

Sounds like you've dislodged one of the vacuum lines off the back of the heater control unit... there's only one way to get at it too. Take the whole fascia off, undo the screws for the cluster, move it to one side (or take it out entirely to give you more room) and then take out the heater control unit and re-attach the vac lines....
And you thought you'd save some time not removing the fascia the 1st time.... It's always the way.

Bastard. Not you. I knew it. It was the same with the Vs's. What an a**hole thing to happen. Your right. Thanks for the advise. Any chance you wanna do it for me?