I already posted pictures and a few words of my HVAC control unit roller wheel illumination modification a long time ago in The LED THREAD for Exterior and Interior lighting, but I wrote new detailed articles regarding my HVAC control unit modifications at E31Wiki.org. My modifications go a bit further than just fixing the dreaded roller wheel illumination...
Whoever drove an 8 series at night probably noticed the inconsistency in illumination of the controls. Especially the roller wheels for temperature and fan speed on the HVAC control unit are barely illuminated. Whether or not you find this an issue depends from person to person, but some people strive for perfection. My articles are meant as a do-it-yourself (DIY) guide for people who wish to fix the bad roller wheel illumination but don't know yet what to expect and where to begin.
[SIZE="3"]HVAC control unit roller wheel illumination[/SIZE]
The roller wheels are illuminated by a single incandescent light bulb. The light is distributed to the three roller wheels by a transparent plastic light bar. This could work, but it would require a much brighter bulb - which on its turn would melt the plastic. A better approach is to ditch the plastic light bar and use LEDs instead. The article describes how to build a new light bar using round or SMT LEDs. The brigtness is adjustable with a trim potentiometer which is positioned so you can operate it without opening the enclosure. Thanks to the dimmer you can adjust the brightness to the exact level you wish - to match the rest of the interior illumination.
[SIZE="3"]HVAC control unit button illumination[/SIZE]
After modifying the roller wheel illumination, it may be desirable to increase the brightness of the buttons a fair bit. I am slowly but surely modifying a lot of controls in the E31 so they all get exactly the same tone of orange and equal brightness. I took the center console seat heating switches as reference. This may be taking it a bit further than required by most, but if you are interested take a look. It's a very simple modification.
The HVAC control unit buttons are dimmer than the reference switches, so a way to increase the brightness had to be found. The buttons are illuminated with BMW orange LEDs. Measuring showed these LEDs run at a very low current, so it's safe to increase the current. A higher current means more emitted light. This is achieved by placing just three parallel resistors onto the PCB as shown below:
The picture below shows the result of both the roller wheel and button illumination modification. The use of BMW orange LEDs ensures a nice matching illumination in the dark.
[SIZE="3"]HVAC control unit button indicator illumination[/SIZE]
The E31 interior - and in fact almost every BMW interior - is illuminated in BMW orange. The status indicators on the buttons of the HVAC control unit are green and yellow, though. I always found this a mismatch, so I decided to replace the original LEDs with BMW orange LEDs to get an all orange look.
The image above shows minature SMT LEDs for the button status indicators which take some practice to solder, but the article also describes the use of the more common 3 mm round LEDs.
(Please note that at the moment some pictures are missing in the articles. I haven't had the time to make these yet)
[SIZE="3"]Alternative[/SIZE]
For those who do not wish to perform the mod by themselves, there's also a kit developed by Martin. The kit is as close to plug-and-play as can be. Of course the HVAC control unit has to be dismantled (you can't go around this - the problem is inside) and two wires need to be soldered.
Martin's HVAC roller wheel illumination kit
For USA/Canada based E31 owners, 1chiban - member at bimmerforums.com - is currently organizing a large groupbuy for Martin's kit. For those who do not want to install the kit themselves, 1chiban will provide a service to do the installation for you...
PnP HVAC Kit - Groupbuy for Martin's kit organized by 1chiban @ bimmerforums.com
No affiliation, but I thought someone might be interested...
