My gauge dimmer bench-tests perfectly and is connected but does nothing. If I remove it, the gauge illumination stays on full (when headlights switched on).
I have no idea where to start troubleshooting this.
The only non-factory things I can see is that the console illumination dimmer has a wire tapped into it that disappears above the speedo.
And -likely unrelated - the parking brake and brake warning lamps appear to have been replaced and are (poorly) connected to a pink + 2 grey wires and a black/white and 2 grey wires: