Hi,  our car has just recently developed a problem, the steering wheel switch stopped selecting manual when pressed, my wife uses it frequently to utilise some engine braking when going down hill. The switch normally cycles round three functions , then it only cycled two functions and now it does nothing. It must control a relay I assume but can find no information in the haynes manual. Any ideas please? Steve.

Do the other buttons on the steering wheel work? Horn, Radio buttons?If not,  should be the Clock Spring behind the wheel.

It still could be it even of the other buttons work, but before replacing it try sourcing any button to replace and use for test purpose.