92 camry 6 clylinder; idiot light for back lights on but all lights work- could there be a sensor to the warning light that isn't working? thanks

 

There is a sensor that can and does fail.

It is possible for the bulbs to work but the sensor triggers if the bulb circuit current draw is too much.

Check the bulb sockets and bulb terminals for rust/corrosion/loose connections that can cause a bad connection (this includes the high mounted bulb) and higher current draw.

If OK, replace the brake and tail light bulbs including the high bulb.

If still a problem start looking a bad sensor (reasonable common failure).