My headlamps on my 172 are set to automatic, i.e. they switch themselves on when it is dark. When in automatic mode twisting the fog lamp switch does nothing unless I manually switch the headlamps on first.
Has anybosy else come across this? If it is a feature of the car then it seems pretty stup that if the headlamps are already on, you have to then manually switch them on to be able to use the fog lamps.