Grant.
I have a 2008 marquis and my cruise annunciator was not responding (turning green) when I would press the ON/OFF switch to ON, this condition was very intermittent, but once on it would stay on. I talked to Monaco and they indicated to me the most likely cause for this is the clockspring in the steering wheel. This device has electrical contacts that can sometimes cause problems. the second item they mentioned is the control module.
What I discovered is that if my cruise annunciator does not illuminate when I select ON, I just turn the steering wheel slightly back and forth and then it responds and illuminates and everything works as advertised. Prior to discovering this little peculiarity, I would just keep trying as we traveled down the road and eventually it would illuminate. In my case I'm pretty positive it is the clockspring in the steering wheel and the contacts may have just a bit of corrosion and by rotating the wheel back and forth ever so slightly it may be making better contact. Some day if the condition persists I may replace it but I' not looking forward to removing the steering wheel to replace it.
As I mentioned, once the annunciator illuminates for the cruise it works just fine from one day to the next, until it decides to be stubborn again.
I hope this helps, good luck.
Larry D.