HELP!!! All My Interior Illumination Died!
 

I just recently put in a new instrument cluster in my 84 500sel (I'm not sure if that had anything to do with this, but it seems related), and now all my interior switch lights and gauge cluster illumination is dead. I checked my main fuse box under the hood, and all the main fuses are fine, but I was wondering if there was a fuse holder between some wires that deal with illumination that could've blown, or if I accidentally yanked out any wires. I can't continue to drive my car at night like this, so I really need to find the culprit! Does anyone know about the wiring of the illumination circuit in a 84 500sel? If this helps, most of the other things on the main fuse circuit, ie right rear tail light, license plate light, and right parking light, are still operational.

The dimmer is in the gauge cluster, likely it's bad.

The aforementioned dimmer plugs into the cluster if I recall correctly, so check to make sure it's plugged in properly. Also double check all the wires to ensure one of the harnesses didn't partially or completely pull off. Check the solder joints on the terminals where the switch plugs into the cluster PCB.

The switch itself is a fairly robust design, so I'll bet it's a loose plug or wire. At any rate, you can find them at junkyards, and I even have a spare good used one if you need it.

Thanks for the help, you guys were absolutely right about the bad switch. I decided to just bypass it, and it can still be brighter even with the bypassed switch, so everything's good now. I appreciate the help; now I can safely drive at night again!

Excellent.

My daughter had the same problem last week; no instrument lights. I told her to check fuses and rotate the dimmer, didn't year back.

Last night she was home, so I went out to the car, turned on the lights, no light buzzer, no dash / switch lights, a few outside lights not working, ... a fuse. Kids, apparently didn't see the black dot in the middle of the white fuse nor notice all of the outside lights not working.

Good job.... I'd replace that dimmer if I were you. This is just a hunch, but I'll bet that MAX on the dimmer is less voltage than with the dimmer bypassed, and I'll also wager a bet that your dash lights, the lights in the window and accessory switches, etc. will not last nearly as long without the dimmer in place. I could be wrong, but undervoltaging incandescent bulbs is an age-old technique for making them last a long time. I would be somewhat surprised if MB engineers didn't exploit that trick.