Got it, something entirely different. In the 124, there is a light control "relay" box behind the speedometer that controls backlighting intensity.

I don't know the wiring by memory, so am not sure whether there is an unswitched power to that box.

The headlamp switch however does have separate contacts for the instrument lighting, and it could have failed closed? It is a job to get to the headlamp switch, need to drop the bottom dash panels to do so, but it does unplug. If unplugging the switch kills the lights you need a new switch. If not, the next stop in my opinion, the dimmer control box.

Have you tried turning the switch further to the left into the "park lamp" positions to see if the instrument lights turn off? Do they still dim/brighten with the rheostat in the dash?

__________________

Gone to the dark side

- Jeff