For those wondering why LEDs done dim with the dash rheostat, it have to do with how LED's work.
LEDs don't dim, they are on or off. This is because it is a diode. When the voltage is high enough it crosses the gap and emits light. Bit more going on than that, but that description will do for this discussion.
In order to dim an led, you need a controller that turns it on and off very fast. That would be a pwm (pulse width modulator) controller. The dial in the OEM headlight switch is, for the most part, a variable resistor. Not what an led is looking for.
When you have the dial all the way up on a own controller, it flashes the led very fast. The effect to your eye is full brightness. As you turn the dial down, it flashes it slower and the effect is your eye perceives less light (dimmer).
I've yet to see an led that dims properly, but some are marketed as dimmable. What I have seem is as the voltage is turned down, the led emits less light because it is at threshold between on and off. It is essentially "flickering". While this may seem to have a dimming effect, what it isactually doing is causing heat to build up in the led and is cutting its life short. Leds don't like to operate at threshold voltage.
Dimming would be possible in a moonie cluster if you were to incorporate a pwm module in the wiring before the lighting circuit.
I did a similar thing with my 98 cluster, but I didn't use "plug and play" leds. I built my own circuits in the cluster and used an inexpensive pwm module (eBay, 10 bucks) to dim them up and down. The dash switch just sends power to the pwm module when the lights are selected on.
Same thing could be done with moonies, but its not an afternoon project.
Here's a video from when I was building it:
http://www.youtube.com/watch?feature=c4-feed-u&v=4uWxZnm0d48&app=desktop
Here's what it looks like inside:
http://www.youtube.com/watch?feature=c4-feed-u&v=T16Tic789dQ&app=desktop
Here's the controller powering just one led during testing:
http://www.youtube.com/watch?feature=c4-feed-u&v=rMlnxCBOjKY&app=desktop