When brake pedal depressed rear brake lights don't work however the one on the cab roof does they also work when flasher is turn on so we have power back up ones and turn signals work-- also have changed brake peddle switch, circuit board under bumper and checked all fuses

https://www.askmehelpdesk.com/cars-trucks/when-asking-about-your-vehicle-303903.html

Stupid question but... are you sure the bulbs themselves are OK? Typically, there are 2 filaments inside a brake light bulb... one filament is for the tail lights and flashers/turn signals and the other filament is for the brake light. Don't overlook the simple things.

Finally gave up and put in dealership shop they can't even find what the problem is but when they do ill post it so all can know
!

Broken or corroded wire or possible bad ground.

They found problem took them 2 days but it turned out to be a faulty plug that the bulb plugged into!