The "aux off" button will do that, according to Matt. The trouble is though, I don't know how to press it, I can only get to the lid that covers it.
AUX button... Master Key in, reverser neutral, brake 3, push and hold AUX button for 5 seconds. Absolutely no mention of this in any tutorial or the manual of course. ps Beware that turning off the AUX systems does more than simply turn off the lights, although I’m afraid I don’t know exactly what it does!