? Is it coming on and not wanting to stay on, do the set lights blink, does it indicate it's on and just not set? The lights should blink if it has a problem, if not check the throttle cable and see if it's loose.
It won't come on until you are at about 40mph and in 4th or 5th gear. the cruise light should be on and when you set that light should be on also. If the set and res flash it is a dealer issue.
I rode to work today and it was 28f out, didn't use it but I have when it's cold and never an issue.