Kenwood head unit doesn't dim with headlight switch

[j_beede]

The double DIN Kenwood unit in my C2 coupe doesn't dim with the headlight switch or the dashboard dimmer knob. The factory gauges do dim down as expected. I can manually dim the Kenwood via the touch screen menus but then it is too faint for daytime driving. The deck (DNX6990HD) is pleasing in all other regards. I just spoke to Kenwood and Crutchfield, they were apologetic but could not provide technical advice.

 

My real concern is that the digital dimming function in the 997 is in some way incompatible with the orange/white wire on the Kenwood that expects (I suppose) a variable dc voltage like it would get form a "normal" car's dash dimmer potentiometer.

 

A visit to my local car stereo shop produced a four figure quote for pulling everything out and starting over from scratch. Anyone happen to have experience with this? 

...j

[jl-c]

As the illumination is by LED's then the dimming is not variable DC but by pulse width modulation. This is varying the amount of time the LED's are illuminated by flashing them too fast for our eyes to see the "flashes" this reduces the average time they are on hence the effect of dimming them. I assume the headunit you refer to is non OE? If so then it will not work unless it has been designed to work with 'dimmed' LED circuits.

[j_beede]

Given the popularity of adding/replacing the factory "stereo" with units that have HD, blue tooth and GPS built in, I suspect that this is an issue that has been encountered (if not discussed) before. 

 

If I can figure out how to pull the head out of of my dash I will "scope" the dimming signal if it is available in the stock radio connector. I'll start looking for a radio connector break out diagram for 2005 997.1 with Bose.

 

If the dimming signal is PWM--as jl-c predicts--then I will build a little ac-coupled DAC to provide the dc levels that the radio (presumably) expects. Based on yesterday's phone call to Kenwood I don't think they will provide the details on what the signalling of the orange-white wire is supposed to be. Surely there is a Kenwood car stereo forum where I can get that information.

[j_beede]

Looks like the Kenwood radio doesn't support variable dimming from the dashboard control. It simply switches from "bright" to "dim" when it detects the headlights are on. This should make debug easier but the end result will not be quite what I expected.