The new light switch is installed and the lights now work perfectly. However, the vent is not back in the dash, because all the speed nuts were sprung (which is why one fell out onto the floor mat). It's crucial that they stay in place in order to secure the vent with the Torx screws. My patent-pending solution:
Actually, there are three speed nuts, but you get the idea. As for my solution, you know what they say — necessity plays with the Mothers of Invention (or something like that). I'll let my invention do its stuff overnight and then I'll wrestle the vent into place tomorrow. (BTW, I wish the stripes in the Porsche crest on the hood weren't cloudy, but the price for a new crest is one arm, one leg, so I guess I can live with this one a while.)