I never knew about the alarm switch either. My 1968 doesn't have one as far as I'm aware. Though I do have an outside key switch behind the driver's seat on the outside "sugar scoop" just beyond the rear window on the upright part. I have no idea what it does.
And Luckyrat - where did you get those numberplates from? I like them and I think I need one saying 1968 Stingray on it too