figured it out....What it (red lighted toggle) does is ground out (through the lighted toggle) the blue (hot) lead coming into the transmission relay. This would have the effect (I presume) of defeating that relay which I suspect is linked to the high altitude sensor. Also, on closer inspection, the toggle is definitely aftermarket and the transmission relay is stock. So someone wanted to be able to defeat the high alt sensor with the flip of a switch. I'll confirm this on my first trip over Donner pass in a couple months. Does this make sense to you tech folks? - Or am I off base here? thanks, Mark