I presume you're using Windows 10. Are you using Minion? If you are not follow perfiction's advice. If you are using Minion in it go to Options then Game AddOn folder Path and point it to your AddOns folder.
I use Minion and installed all my AddOns on a seperate drive as well.
From -->
C:\users\<your user>\Documents\Elder Scrolls Online\live\AddOns
To --> G:\Libraries\Documents\Elder Scrolls Online\live\AddOns
Note that I manually pointed all the contents of my Libraries folder from their default install location to a different drive in case my OS takes a powder, etc...
perfiction wrote: »ESO will always look at C:\users\<your user>\Documents\Elder Scrolls Online\live\AddOns
If you want to have your addons folder on different drive then you have to make a link (mklink command)