On the back of my new CM Stacker case there is a small toggle switch at the bottom right corner clipped into the case and inside it has a two pin female motherboard header connection it is labelled "INT SW". I'm guess that means INTernal SWitch, but what is it for?
it probably not it but could it be the chassis intrusion switch? i know my motherboard has 2 pins on it so a chassis intrusion switch can be installed (when the case is opened while on the computer sounds an alarm...)
have a look in the manual http://www.coolermaster-europe.com/installation_manual/CMstacker_manul_en.pdf have you followed the wire to see where it ends up?
hmm yeah you could unless you meant (in your older post) that it had a wire coming from the switch to a connector labelled "INT SW" is there anyway the switch would be flicked/toggled if the side panel/door was opened/removed? If so then i'm almost certain its an intrusion switch