It is under the display settings in the 8.4 uconnect under "fuel saver in cluster". However one of the last software updates made it so you can only see this option after doing a software update.
So the process is this:
1 Update the uconnect system (theres a ton of videos on youtube on how to do this)
2 When the update is finished the 8.4 will reboot.
3 When the 8.4 comes back up immediately go into the settings under display settings and make sure "Fuel Saver in Cluster" is checked.
4 Turn the key off and then back on.
5 Eco light should be in the cluster when driving economically
As far as I know this is the only way to get to this setting. Also as mentioned, the Eco light does NOT indicate MDS is active, it simply indicates you are driving economically.
Hope this helps!
