Just to the right of the steering column and in front of your right knee is a switch. Turn it off and all your lights will magically start working again.
It is in the same block of switches as the coupling light but is the extreme left hand one and easily caught when putting the key in the ignition for example and the chances are you didn’t even see it when you were trying all the light switches as it is so tucked away.
its very logical, you can turn your cab light on to see where your going in the pitch black before you even start to climb the steps, instead of some trucks where you have to get in and then hunt around for the switch, its right there infront of you.