So I'm experimenting a bit with an artificer/wizard character. On the artificer page, it says that one can either use artisan's tools or thieves' tools as an arcane focus, or one of your infusions. 

My question is, if I make a wand of secrets with my infusions, can I also use that as an arcane focus for my artificer spells?
Can I also use it as a focus for my wizard spells?

You can most certainly use it as an arcane focus for your Artificer Spells. I'm pretty sure you can use the Wand of Secrets as a focus for the wizard spells, too. It is still a wand and should therefor be usable.

That said, i think a better way is to use the Enhanced Arcane Focus - which too can be used for both classes as a Focus.

Thanks a lot! 
The reason I'm using a wand of secrets is because I want to,, y'know, use the wand of secrets? It just fits the character better.

The Wand of Secrets, as an infused item, qualifies as a spell focus for artificer spells.

The Wand of Secrets, as a wand, qualifies as a spell focus for wizard spells.

Note that by a strict (and obnoxious) reading of RAW, only wizard spells with an [M] component can be used with a focus.  Everything with just [V] and/or [S] components needs a free hand unless you're a War Caster.  The wand will, however, be useful for all artificer spells as artificers explicitly add an [M] component to any spell they cast.