How to Turn It On
The anti magic plants you see scattered around that area you just need one.
You can also place them next to the magical turrets to shut them down. The down side is carrying them nullifies your spellcasting within a radius or even getting near them.
Once you restore power all the turrets power down. They have no other use except maybe creating a permanent anti magic zone but carrying them effects you.
Note: The tower’s best usage is the chest that you can find with a perception check. Pick that damn chest up and put it in your inventory and never drop it again – all items you put into it the weight of them is set to 0. But don’t put items you have a use for, other than seeing them, it’s hard to find them in that chest because it transforms them into a special item and transforms them back if you pull them out.