Has it ever worked? Took me a while and a friend to show me how to use mine (coming from classic cars owner history)
Set - - - Is visible with the green light on and off I think whilst scrolling through the computer (end of right stalk) Then whilst green icon lit, select speed on left steering wheel and then once correct, hit the R over the right side of the steering wheel.
I believe you can just tap + + for speed increase and it will knock it on too if you haven't tried that...Make sure you're over 20-25mph too?
Sorry if doesn't help, just firing info out to try and help
