[Airjer_]

The brake and turn signal use the same filament in the bulb. Since the turn signal works we know that the wiring from the switch to the bulb is good. We also know that the brake light works on the other side so the brake switch and wiring to the turn signal switch are also fine. The only thing left is the turn signal switch.

While pushing the brake pedal wiggle the turn signal switch and see if the brake light starts to work. If it does you just confirmed a bad turn signal switch.