Hi lars.
It“s correct you have to modify the above.
What you do is take the gauge out, look at the back, there is 3-legs, and the lower one, you can se a resistor on the plastic plate in brown, you have to shortcircute it, take a wire and solder it to the back where the legs come out.
job done
If in doubt, follow the green wire from the plug on back off the dash bord, to the gauge, it will show you what "leg" to use