1999 Toyota Camry backup lights and license plate lights don't work?
Check the wire loom that comes from the passenger part of the
car to the trunk. You will find it in the trunk by the driver side
hinge. The wire loom flexes at the hinge every time the trunk is
opened and closed. Look right where it bends for broken/cut wires.
From radio-shack buy crimps (18-22 gauge/eight of them for $3/-)
and a cimping tool ($8/-) to join the wires and get it working
again -- make sure to match wires using their color codes.
(It is quite unbelievable that many car owners will experience
similar issues. My hunch is that your last major car repair shop
has something to do with it. In my case I'm quite confident that it
was the car dealer who did it on purpose when they performed an
unrelated service on my car. The dashboard waring sign about the
back-lights appeared within a month after that and after many
months I realized the reason for the warning sign.)