Hi and welcome to Ninjette!
Do you have multimeter?
Interestingly enough tail-light fuse#4 only powers the license-plate light and brake-light (going through both front & rear brake switches in OR circuit). Tail-light itself is powered from ignition-switch TAIL2 terminal with no fuse in between. Issue is either defective ignition switch (extremely unlikely), or something wrong with wire between ignition-switch and tail-light.
This is 5-minute fix with multimeter.