Improving Instrument Cluster Lighting in a W126

[mmitch]

I thought I would share my relatively painless fix to the poor instrument cluster lighting in my 1987 300SDL. First, my cluster instruments are all VDO electronic, so once the cluster pops out, it is easy to disconnect all electrical connections but remember to start with disconnecting the positive lead on your battery. Other posts have indicated all sorts of problems with electrical shorts if you work with the main power on.

Take the cluster to your workbench and remove the speedometer to see the state of the two cluster lights, their housings and the clear plastic prisms that are the optical way the light bulbs project light to the front of the instruments. It looked to me like the optical equivalent of communicating with two tin cans and a string.

My prisms and housings were clearly melted from the previous owner frustrated with the dim W3W bulbs. He tried W5W bulbs which melted and darkened the heck out of the ends of the clear optical prisms and only produced less illumination but alittle smoke as well.

After an initial frustration with the German optical engineering, I thought about swapping out the optics and going to hardwired LEDs that I read about in this forum and other blogs. They would surely brighten the instruments. But I thought the Germans have not let me down on other engineered parts of the SDL, so I rethought their optical solution and tried to work with the burned optical plastic. I removed the clear plastic lenses which can be had by opening the two white covers on top of the cluster. I got my Dremel tool out with a drum grinder bit and a soft polishing bit. I ground away about a 1/2 an inch of bad plastic and recreated a slightly shorter concave surface which included a 45 degree downward angle for an edge. I wanted the light which is sightly below the prism to capture all the light it can. I then gently polished the ground concave prism end. You can get it to a very high gloss with using alittle rubbing compound on the buffing polishing bit. So the prisms are alittle shorter but just as clear as new. I took the suggestion of others on the forum and used LEDlights.com 194 T10 wedge SMT Super Flux 5 LED Blue lights. They plug right in and are actually four LEDs, one on each side of the square and one LED on top pointing forward. Just remember that LEDs have polarity and you may need to reverse them if they don't work the first time. My cluster illumination is a light blue and is just right. It doesn't blast you out. It is easy on your night vision and you can easily see everything from the fuel gauge to the clock on the far right. I guess German engineers knew what they were doing in the first place.

[Dee8go]

Not to hijack your thread, but I noticed the light on my instrument cluster is pretty dim at night. I don't know how similar the clusters in tese two models are.

[mmitch]

should be very similar. in fact, just clean and buff plastic prisms and W3W bulbs will give the white/amber light that work better than blue LEDs.

[MTI]

This is what 5W bulbs can do to the plastic "prism"





Here's one alternative I'm doing. It's basically removing the prisms and replacing the system with an array of LEDs, wired to the bulb sockets so that they can be dimmed and adjusted.

[Dee8go]

That's pretty cool. LEDs don't throw off any heat at all do they? I bet the light is both brighter and more even with LEDs, too. Did you buy them in those strips? Where do you get them?

[MTI]

LEDs won't generate as much heat however, withoug diffusion they have a limited dispersal area, so the five unit array was needed. During a test fit and power up, the illumination was pretty even.

The "sticks" were custom made on pc board with the resistor to match the LED values by a guy that used to sell them, but I haven't been able to reach him since. As you might guess, there's more than one way to afix the LED array.

[Chad300tdt]

Originally Posted by Dee8go

That's pretty cool. LEDs don't throw off any heat at all do they? I bet the light is both brighter and more even with LEDs, too. Did you buy them in those strips? Where do you get them?

Dee8go,

The LEDs from ledlight.com are very bright, need no modification to work and are completely dimmable. Here is a link to the bulbs you need.
http://www.ledlight.com/SearchResult.aspx?KeyWords=45689

Heres a pic of my cluster with the LEDs from ledlight.com:

[Dee8go]

Yeah, that looks great. Thanks, Chad.

[crhenkel]

Not only are the LEDlight 5 led bulbs so bright that I have to dim mine, they give off almost no heat. You still need a good clean light prism to transmit the light so if they are melted, just polish them up and it will work great! For those of you that are looking for custom, you CAN get the led bulbs in red, amber, I think green and maybe UV. I love my clean bright white ones.
Enjoy!