I'm no engineer either, but I am an electrician. The dashlight dimmers on older US manufacturers were wire-wound potentiometers (pots, for short) and commonly had a point where the lights went out entirely, rather than keep dimming gradually. If one were to keep rotating the pot all the way to full off and then back to increase the light level, they would be able to get the lower light levels. Same thing goes for lighting dimmers in your house - unless you paid the few dollars more to get the better dimmer with aq PC board inside. The pots in those units (just like your Volvo) use a non-wirewound pot.