Generator Switch - Item No. or Location.

[Silverblade]

I've completed three of the four ward locks preventing me from going further into Durlags Tower. The last one remaining is the Dwarf that want a bottle of wine. I found the grapes, the Wine Press and The Generator.
The problem is, I found the switch when I entered the tower but disgarded it mistaking it for a magical bolt. Not being equipped with a Crossbow and you can't sell them anyway I dropped it. When I realised what it was (After a few saves) I went back for it, but it was gone. I need either;
The item number of the switch so I can equip it and continue.
Or the exact location where it should be. (In the bookcase in the room north of the wine press). I think.