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Is the owner's manual wrong? Does your dash brightness controller adjust the OEM radio button brightness?

11 January 2021
Ontario, Canada
While trying to fix my 2001 radio, I looked at my 1995 NSX and I noticed a few things with its radio illumination that I hadn't noticed before, that don't agree with the owner's manual:
  1. With the radio on, turning on the headlights both dims the display (and the radio station indicator) and also turns on the button and knob illumination, as expected.
  2. However, when I rotate the dash brightness controller, the radio buttons do not get their brightness adjusted like the climate control buttons and knobs do. The owner's manual says that this SHOULD dim the radio buttons as well, but it definitely does not in my car.
  3. Looking at the electrical manual wiring to the radio (red/black to A3), I can see no way for this to be accomplished, as red/black (running lights) sends the binary signal for illumination or not, but the variable intensity seems to be driven by a variable connection to ground in the dash lights brightness control. This variable ground is a red wire, which goes to the CC unit and a bunch of other switches that have their brightness controlled by the dimmer, but NOT the radio, which only gets the red/black on/off signal.
  4. Looking at the owner's manual, I see that there is also a separate feature to shut off the illumination of the radio knobs and buttons, by pulling out the balance knob 1 notch. (Anyone else remember that from reading the manual?) Could this be the replacement for the dimming feature since perhaps Alpine didn't offer a radio that would take a variable ground input for button dimming?
  5. (When I turn on the radio with the headlights on, the illumination of the eject and dolby buttons turns off, presumably because I don't have a tape in the deck so those buttons have no function. Brilliant!)
My two local NSX buddies have aftermarket head units. Anyone with a stock OEM NSX head unit willing to check if their radio behaves differently than mine and like the manual says it is supposed to? I believe the USDM head unit is identical for 1991-2005.
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My stock radio behaves the same way. No dimming with the dimmer switch. If I pull the balance knob, it turns off all button and knob illumination. Display illumination functions normally, bright when parking lights off and dim when parking lights on. With parking lights on, the pre-set buttons illumination also turns off when the CD function is used.
I believe the 4P connector to the clock also does not have a variable ground wire so the clock behaves the same as the radio with only bright/dim.
I believe the 4P connector to the clock also does not have a variable ground wire so the clock behaves the same as the radio with only bright/dim.
That's correct. No red wire so the clock doesn't adjust brightness with the controller either.

The error is present in the 2001 manual. No-one noticed the mistake and corrected it in more than 10 years? I don't think they changed the USDM radio over that time and I doubt they changed the manual from correct to incorrect. It probably persisted all the way to 2005.
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