I finally couldn't take the dim dash lighting in my '86 300e. I could only see the top half of the speedometer and gas guage. This was even after installing new 3W bilbs and cleaning the light prism faces.
Using an idea I got either from this forum or from the Brickboard (can't remember which), I removed all the original plastic prisms and installed LEDs. The results are really great. Now I can see even the numbers on the trip odometer. The posted photo below shows the new lighting fairly well although the lighting is actually even better than you see in the photo. Upon examining the plastic prisms, I could see that the 'capture area' where light from the bulb enters the prism is quite small. The efficiency of this system has to be low.
If there is interest, I'll go into more detail with pictures. That is assuming I learn how to attach pictures.
Briefly, I pulled the cluster out, used a Dremel to grind out the plastic welds holding the two prism covers, removed the old yellowed prisms, painted flat white around the slots where the prisms had reflected light back to the guages, and mounted two, white, LEDs in each slot. The LEDs are powered by a 9v regulated supply which draws 12v from the dash light dimmer supply. I also painted the guage needles with a fluorescent orange model paint which I bought at a toy store. The total cost was under $5.00.
