the manufactories change one resource into another, and are inefficient - itd be pointless to have them all running at once. If you need one resource and have space of the other, they will turn on though
So they are fully automated in that sense then?
If I were to override it accidentally they would revert to off as needed?
Yes and yes. Also, while this shouldn't happen unless you're wanting to do something tricky, if you want to stop the automatic logic there's a control node for that.
Thanks for the 'L' tip as well.
L is worth it's weight in gold. Shift+L is also useful, it takes 1/3 instead of 1/2. Note that you can press these in sequence, so L,L is 1/4, L,Shift+L is 1/6, etc. If you want to split them off from their control group you can do alt-shift-# (iirc). In the betas there's a context menu command for splitting your selection across multiple control groups which is great if you actually want to create (for example) 4 subfleets of roughly the same composition. Granted, it's clunkier than it should be (beta, etc), but it does give more precise results for fewer overall keypresses, in general.