The third brake light is working , are the LEDs broken ?
If the stock ones dont work either, probably stop lamp switch on brake pedal. Or wiring from stop lamp switch. Get a schematic diagram of the exterior llghts and multimeter and go over the wiring.
The LEDs are not burnt out because they do work when the car is turned on and the headlights are turned on.. However when braking, they do not become brighter or indicate a stop in any way, we think it could be something to do with the bulb, since when we put them back into the stock tails they would not light up when braking either.
Did you take the stock control box (on the left outer wiring harness) out and replace it with the connector with the resistor on it?
put in wrong, ib.
take one out and flip it 180.