So my brake lights all work until I turn my left blinker on and then the right brake light goes out. The blinker works and top (rear window) brake light stays on. Problem is not symmetrical, with the right blinker on the left brake light stays on just fine. Already tried replacing all brake lights and turn signal lights as well as the turn signal switch (multi-function switch). Still same problem. They won’t let me pass inspection! any suggestions???
You might try replacing the flasher unit and see if that helps.
Check the grounds at the rear of the car. Alternatively, just run a (fairly large) ground wire from the front of the car and ground all the rear lights to it.
Are the brake lights and turn signals different bulbs?
Year, make, model is always helpful…