outside, the running lights and brake lights are fine. But inside, the overhead lights of the rear shell are all dead. (The rear bed, the hallway, the bathroom, and two overhead lights mounted on the rear shell, just behind the front-shell mounted A/C).
Fuse is good. And most strange of all, I unscrewed the safety switch under the bathroom door-- it's got 12V (13, actually), and properly goes to zero differential when I push the switch down. And even shorting the leads with the screwdriver doesn't turn the lights on.
Help!