What you write may apply to the Z3 and Compact. A E36/2/4 dimmer unit, however, does use Pulse Width Modulation, but with a linear, ca. 20-100% dimming curve meant for incandescent lamps. To provide uniform and sufficient dimming, a PWM dimmer for LEDs needs a non-linear (exponential or square-law) dimming curve that ranges from nearly 0 to 100%. I couldn't find a suitable automotive LED dimmer when I looked a few years ago, and ended up designing one to dim a pair of 10 mA LEDs in series.
You face the same issue when you change the interior lights to LED. I square the linear, PWM, ramped lighting signal from the ZKE (and change, say, 10% on to 1% on) which seems to do the trick.
Last edited by johnf; 12-10-2012 at 10:10 AM.