Instrument Cluster Lights Not Working on 81 300D

[johnbob]

Yes, yes, yes, I know this has been covered numerous times but I can't seem to find my exact situation, so please hear me out.

I have a W123 1981 300D non-turbo sedan and the instrument cluster lights are not working. I'm talking about the two main lights on the top of the cluster. All the other lights work properly; the warning lights at the bottom of the cluster, the lights in my center console (AC/heating, etc.), the PRNDSL in the shifter, the headlights, fog lights and the blinkers (in the cluster and the exterior of the car) all work. It's just the main two cluster lights that don't work.

Here are the things I have already tried:

- 3 different dimmer switches, including one that has been bridge-wired.
- 3 different fuel gauges
- 3 different clocks
- 2 different instrument cluster housings
- LED light bulbs and a few sets of traditional bulbs
- 2 headlight switches

Anyone have any other suggestions? From my understanding, it wouldn't be the dimmer switch if all the other lights were working, but as I stated above, I tried 3 different ones anyway.

The one little quark I've noticed, the glow plug light will flicker back on from time to time while I'm driving.

I assumed that I must have shorted something out, but after swapping pretty much everything, what else can it be? What am I missing?