Dang!
OK, well it's a sunvisor light from a scrapyard VW that was mounted in the headliner above/behind the sunvisors (I think this was from a Passat, but many VW's have them). Cost me $5 from the local You-pull-it, but you can get them - albeit, more expensive - off eBay. here's an example:
http://www.ebay.com/itm/For-99-00-0...unvisor-Dome-Reading-Light-Lamp-/130822597048
It's placed over at the side, because that's where there's space above the Mazda's headliner with a cutout where the wires are routed into the rear door. And yes, I simply extended the wires and ran them across and down & attached them to the wires supplying the side trunk light.
I also replaced the old festoon bulb in the VW light (which is quite dim) for a couple of strips of 5050 LEDs.
More photos:
View attachment 203177View attachment 203178