Power from Taillight is wired to fuel sending unit... Check!

Maybe related to that, I am missing the final pigtail to the right rear lamp, and the key was not in the ignition. But I would think with the ignition off, there should be no power except to the horn, hazard and light (because those typically work whether the key is in or not).

BTW I'm testing for voltage by touching the tester wire to the wire and the other lead to the body of the car.