Well you can pretty much determine that it is the switch if both mirrors will not go down, it is unlikely the motor is broken on both mirrors. I would get pricing from a couple of dealers on the switch, and ask if it is a common failure item when you call. Make sure you get your MBCA discount, that helps a lot. I don't know the new S that well as far as replacing the switch, I think I remember it being in the door? Good luck!
Brian

__________________
Brian W. Heitman

www.MBCA.org/northtexas

Join MBCA!!!