Alternately, you can madmax it like me. I run my brake lights directly off an old ebrake lever switch. (used to use a 1985 Honda scooter brake lever; the switch finally became unreliable after 30+ years of original + my use, and the hinge was floppy).
The way I do them is that I have LED taillights that run all the time at low brightness, and brighten during braking. I also have separate brake lights that run only during braking.
Simple dimming is a big power resistor (or several paralleled / seriesed, to get the necessary resistance and wattage), placed in series with the +12V (really +15V average) to the taillights, with the other end of the tailights to ground.
To keep the brake lights form coming on except during braking, and allow brightening of taillights for braking, there's a diode installed with it's stripe toward the taillights +V from the resistor, and the other end to the brake light +V wires. The other brake light wire goes to ground.
The brake switch is wired across these, so it allows full +V to both lights when the lever is pulled. I am presently using a separate lever for the lights (vs the controller ebrake signal), so there's two brake levers on the left side, but you could easily add a switch to any brake lever in a number of ways, or use a relay to engage brake lights and ebrake.
Because my camera autoadjusts for brightest stuff in scene, you can't directly compare the brightnesses of the lights, but if you look at the interior light of the cargo hold / dog carrier, or the red downlighting of the ground at the back, you can see how much dimmer it is in the "on" pic vs the "off" because of the camera dimming the whole image to compensate for the brake ligth brightness.
https://www.endless-sphere.com/forums/viewtopic.php?f=2&t=67833&start=775#p1424309
Brake lights off:
Brake lights on