Not sure which switch you're referring to but, if it's the one to turn on the cockpit light you put up near the canopy handle, mine comes on when I turn on my nav lights. I have D1000T not the HDX but mine isn't related to the Dynon at all.
Port Orange, Fl
RV-12 N121TK ELSA #120845; first flight 06/10/2015
RV-12 N918EN ELSA #120995 Eagles Nest Project
SPA Panther N26TK in progress