I wish I had a nickel for every light failure that did NOT involve a burned-out bulb!
You need daylight to chase this down and a meter is helpful also. For the
brake light you can short across the switch (so you can do it without a helper)and then check the socket with a meter. If the juice is there, scrape the socket
and the bulb surface. They are famous for invisible (or visible) nonconductive films.
If not, see if there is juice at the switch, then chase it back to the fuse box.
From what you did, it sounds like a ground failure at the taillight, so you may
need to check that out also.
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George Downs Bartlesville, Heart of the USA!