[40cpe]

I would find the brake light wire at the tail light bucket and verify that it is hot when brakes are actuated, both with headlights on/off. Then verify that the brake light hot wire is connected to the brake light section of the LED light. As jSeery said above, if the tail light wire is connected to the brake light section of the LED cluster, you won't see when the less bright portion (tail light) is activated by the brake light switch.