Originally Posted by wpoll

I'm trying to keep my electrical explanations "conversational" rather than go full-on "electrical engineer" on everyone!

But yes, of course.

While caps would "average" or smooth the PWM pulses, reducing the forward voltage on an LED doesn't produce a brightness variation in the same way as would occur with an incandescent lamp, so the system would need to be reconfigured to give good tail and brake values.

Which I think can be done via BMW Scanner but I'm not familiar with what PWM values result in good brightness levels for LEDs.