The normal Torx screw has a recess that accepts the tip of a Torx driver. An E-series Torx screw has the gender reversed: the screw has the male part, and you need a socket to fit it. They're damned rare; I'd never heard of such a thing, let alone seen one, until I started on this job.
I thought I was going to have to spend $51 for a set of them, but I got lucky. The local NAPA auto parts store had just the E4 socket I needed for $5.
I got the switch done and the truck back together too late to get where I was going yesterday, so I stayed here one more night, and am about to hit the road.