1999 silverado Brake light problems

My third light works on right side but not left side and both of my stop lights are out???????Fuses and bulbs are good.....need some help

if you just looked at the bulbs that might not tell you if they are bad... either test them with an ohm meter or replace one of them.. if they are in fact good id say you have a ground issue or a bad brake light switch.. you need to verify power at the sockets.. i think some of those trucks had problems with the tail light circuit boards so check for power at the connector if you dont have power at the socket

dont have power at the sockets ...where is the tail light circuit boards located at thanks......