Vectra xenon headlight fault

Hope some of you experts out there can help with this problem, as you have with others in the past. Car is a 2001 (just out of warranty, of course) Vectra 2.2Dti CDX with xenon headlights and the associated automatic headlight levelling system. A few times, always after going through the carwash or after a drive in wet conditions, the offside headlight fails to come on and I get a message on the display unit saying something like "Low beam fld/vision" (sorry I can't remember it exactly, if that's not right). I've swapped the bulbs around to check that they're OK but it's always the offside light that fails to work. I'm trying not to think about expensive electronic modules just yet and hoping that there might be a dodgy connection somewhere, possibly related to the levelling system. Any ideas? What do you think? And in any case where might these connections be and how would I recognise them? Sorry if it all sounds a bit vague but thanks in advance anyway.