If you've lost your instrument and dash illumination, the likely culprit is a malfunctioning rheostat (dimmer switch).
Try to turn the adjustment knob a few times to see if you can get the lights to work in any position.
To fix this you have to take the instrument cluster out.
Had the same issue with my 500SEC; pulled out the instrument cluster, changed the 3W bulbs (got from performance products) and put it back. THe instrument illumination lights are working.
Had to turn the rheostat lever a few times; saw some dust coming out , everytime I turned. anyway, it started working after this.
Have plans to buy the white dials on offer in the ebay and change the dials.
BTW, the catalog from Performance products is very informative; from the gaskets for the engine to cosmetic products for Benz cars, man, they have a range of products on offer.
In the meanwhile, I want to have the temp. display for my 500SEC. It does not have one now.
I have the temp. sensor cable that leads upto the fuse box; there it connects to a two core cable.
What goes to the other end of this cable in the instrument cluster?
Any info will be appreciated.