940: Instrument Panel is dark

Hello everybody,

the background lightning of the instrument panel of my 940 (1994) is
dark (Odometer, all buttons, cigarette lighter etc).
It might be a problem with the dimmer, as all lights that can be
controlled with it are affected. The fuse is ok, all other functions
related to it are working fine.

I unmounted the dimmer-knob and measured the resistance:

I see four contacts, numbered 1,2,4 and 6

Pin1 to Pin2: 1,13 -> 0,30 (switch from low to high)
Pin1 to Pin4: 0,02 (independent from switch)
Pin1 to Pin6: 1,38 (independent from switch)
Pin2 to Pin4: 1,15 -> 0,32 (switch from low to high)
Pin2 to Pin6: 0,24 -> 1,08 (switch from low to high)
Pin4 to Pin6: 1,40 (independent from switch)

I then measured the voltage at the plug in the car.

I tried to settings,
1. Key 0, all lights off
2. Key "0", position light on
3. Key "II", headlights on

setting 1: No voltage at any pin

settings 2,3:

Pin 1: 12 V
Pin 4: 12 V
Pin 6: GND

I am a complete dummy when it comes to electronic, so any help in
solving this is highly appreciated.

My question is: Is the dimmer switch working correct or not?

If it's out of order, which contacts do I have to connect to get the
lights working without the switch?

Thank you!

regards, Thomas