Product review (5 stars): The cheapest repair you'll ever encounter for a SubZero fridge!
Pretty straight forward to replace (though you have to remove several screws and a couple of metal parts -- be sure to kill the power to the fridge first!).  Also provides a good opportunity to vacuum out the upper area of the fridge.  This switch looked just like the one it replaced.  I knew it was bad because the old switch still worked for a while if you wiggled it a big, and then got to the point where we couldn't get it to work any more.  There's a detailed page showing replacement instructions which you can find if you search the web for "change a sub-zero light switch".  I'm guessing this would've been a $300 repair if I called the SubZero repair guy, and instead it was under ten bucks!  Note there are several similar switches available but this particular one was not only cheap, but offered free Amazon Prime shipping.