The other day I updated the AirPort Extremes in my house, resetting them to their default settings. When I had everything up and running again, I noticed they no longer flashed with activity. I searched through the AirPort Utility 6.x (6.3.2) installed on Mavericks and could not find this setting. I searched DuckDuckGo and found a lot of other people longing for this option, too. Since you cannot install (can you?) AirPort Utility 5.x onto Mavericks, I ended up installing 5.x onto my Windows 7 VM. There I was able to find the setting, make the change, and was happy again.
But what if you don’t have a Windows VM? What if all you have is Mavericks? Well, I have an easy enough solution for you. In AirPort Utility 6.x, export your AirPort configuration file and save it to your desktop. Open this file with a text editor (such as Sublime or vim) and search for “leAC” (lower case L).
Change this to:
Save the file, go back into AirPort Utility 6.x and import this configuration file. Don’t change anything else in your file, just the 1 into a 2. This tells your AirPort that you’d like it to “Flash on Activity”. Let the AirPort restart and take note and the wonder that is a flashing green LED.
It seems this trick does not work on the latest Airport Extremes with 802.11ac. Even with the above set, the LED on the front of this device does not flash.