So when I bought this car the Instrument Panel, Console Lights, Shifter lights and most of the Cabin lights (except dome light and a two lower door lights) were all dead. I've tried a bunch of different things based on other threads to chase down the issue but am all out of ideas, any direction is much appreciated.

The strange thing is the warning lamps in the panel all work, turn signals, brights, glow indicator, etc. And some console buttons light up when pressed, like hazards and defrost and whatnot. But otherwise the car has no interior illumination, it's pitch black in there while driving.

Here's what I've tried so far:
-replaced all fuses under the hood
-checked OVP, seems fine
-pulled Instrument Panel, changed potentiometer and all bulbs. Looked to replace red panel fuse but mine didn't have one
-replaced all cabin bulbs

I feel like there's one "thing" or controller or fuse relay that is causing the issue, though that may be wishful thinking. Thanks for taking a look.

If there isn't a fuse for interior lights you might have a bad headlight switch.

[edit] Can't be the switch if the park lights work. ETM shows the park light signal goes from the headlight switch to the exterior lamp warning module with a branch for interior lights. There's a path to the ashtray light which bypasses the rheostat. Does your ashtray light come on?

There are 2 grounds for interior lights - W1 on the left edge of gauge cluster cavity and W12 ahead of and to the right of the shift lever. Mind the airbag control module!!! A working ashtray light acquits W12.

Sixto
87 300D

Thanks sixto I'll check that out. The headlight switch itself does what it's supposed to right now, in terms of turning head lights on/off, but I guess there could still be something shorting out the rest of the stuff.