Backup lights do not work. on 2003 Toyota Tundra

Fuses checked, all other lights working. Is there a sensor that can be changed?? thanks

Asked by for the 2003 Toyota Tundra
are the bulbs good
yes - changed one just for kicks and inspected the old bulb - filament was intact.
ck pwr and grd wires to start with
Will do - forgot to mention during the last recall for the frameinspection the dealer removed the bed and sprayed the frame and reinsalled the bed. Is it possible they didn't get a good ground?
yes there might be bed liner between grd strap and frame or they left it unhooked
Will try to locate the ground wire/strap.... thanks for the tip!