Four way flashers are working fuses are good
bulbs are good third brake light is working turn
signals are working
So reading into this question, assuming you are having a problem getting the brake lights to turn on by themselves, sounds like you need to change the brake light switch on the brake pedal. This would cause them not to work.
But my third brake light on cab is working
Yes, but that is a different circuit into the brake light switch. Your blinkers are working, hazards lights, those light up the brake light filament which is the same as the turn signal filament in the bulb, so the wiring to the rear of the vehicle is good. Now there is a brake light fuse that should be checked along with a brake light relay. These items also could cause the problem. All inexpensive items.
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