Hi, on our lunar we have the panel above the door which contains the lighting and heating controls. To the very left there is a button which can be in the 0 or I position.
We can't find it in the book and can't remember what the dealer told us about it. So far we have only been stocking the caravan with our things so if we put the lights on it's been via the battery not EHU as we are in storage. This button doesn't seem to make a difference to the lights as to whether it is in the 0 or I position.
We had a similar switch in our Ace Award. In the I position, it turned on a small light above the mirror opposite the door. It was there to give a little light when returning to the van in the dark. If it is this, I think you will find it only works when on EHU
Have a look to see if it switches a light on in the shower cubicle or washroom. We had a similar problem when we first bought our caravan wondering what a rocker switch by the entrance door was for. It wasn't till my wife wanted to go in the shower one evening and wondered how you switched the light on!
Thanks for the replies. Dealer finally got back to us. The reason it's not in the manual as it was an extra. Explore you were right. It turns on a light for the front locker.
Update. The switch does not operate the locker light, that is a switch in the kitchen. It does however light up LED lights behind the front handles. Mystery finally solved.