I had not noticed the green LED until reading this thread but it is there, between the two Acuralink buttons.
In my case it comes on shortly after I open the driver's side door. I have not noticed it at night so I don't know whether it is on then or not. I have not found anything from Honda, Acura, or Acuralink that specifically addresses that but in reading threads in an MDX forum the thought is that it indicates connectivity to Acuralink. A couple of reporters in the MDX forum said that their light turned red and they had to take it back to the dealer to have Acuralink rebooted. At least one person indicated that they thought there had to be cell phone connectivity for it to be green. I can confirm that cell phone connectivity does not affect the color. I turned my iPhone off and left it in the house while I went outside to observe the LED in my TLX. The LED lit a solid green. I suspect that a solid green indicates that Acuralink is functioning properly. A red indicator means that it is not functioning properly.
I have a "driver education" workshop with my dealer on Thursday evening. I'll try and get a definitive answer then and report back.
