Illumination and dimmer explained?

Would someone be so kind as to explain what the Illumination/dimmer is in a newer vehicle? Newer being 2000 and up. Also, would it be possible to get an explanation of polarity (if D.C.) or pulsed (if A.C.) I know many times we dont use this particular wire, but I think the overall understanding of the wire is lost. Thanks

The illumination wire gets 12 volts whenever the parking lights are on, and dims the deck's display a predetermined amount. A dimmer wire will dim the display in correspondence with the position of the dimmer switch. A positive dimmer wire will start at 12 volts with the lights on, and eventually reach ground as the dash lights are dimmed to max. A negative dimmer wire does the opposite- starts at ground with the lights on, and reaches 12 volts with the lights dimmed all the way.My ex once told me I have a perfect face for radio.

thanks for your time, I am seeing something called PWM, pulsed width module. I think this is going to be a little different then a simple pot. What do you know of this PWM?

Honestly, you probably know more about it than I do. However, if you tried to hook up a pulsed signal to the dimmer wires on your head unit, the display would probably appear to be blinking.My ex once told me I have a perfect face for radio.