Hi Ian!
I'm sorry to hear your new light is not working properly; how frustrating!
It may not be your fault.
Sadly, water-intrusion and lamp-switch control issues has been reported elsewhere by others in online Fora and vendor buyer reviews, especially in Germany and among the randonneur community. Judging by the reviews and user experiences,
not all are affected, but a small percentage from some production runs are. Early production examples seem to exhibit more problems.
I would suggest contacting first the vendor and then B&M to see what suggestions they can offer, and if this is something that might be covered by basic warranty. After all, when you were caught in the rain, you had either the little flap-cover closed or the plug firmly in place, so the light should have remained dry.
Meantime, if you happen to have a bag or box of rice, try detaching the lamp and putting it in the rice. The rice will act as a natural desiccant and absorb some of the moisture. It is a long-shot, but sometimes works with cell-phones that have been immersed. Just be sure to avoid getting any rice grains inside the cable port.
Here are some links to others with similar experiences. Perhaps something in their discussions might help:
Here; about halfway down the page:
http://positivo-espresso.blogspot.com/2013/01/led-headlight-reviews.htmlhttp://www.bentrideronline.com/messageboard/showthread.php?p=1092958Look at the reviews at Rose Versand. There have been other reports of water intrusion there.
Later production models of the light have come with an informational paper leaflet from B&M that can be seen/translated here:
https://yacf.co.uk/forum/index.php?topic=63183.msg1469353#msg1469353https://yacf.co.uk/forum/index.php?topic=63183.msg1470627#msg1470627https://yacf.co.uk/forum/index.php?topic=63183.msg1470738#msg1470738https://yacf.co.uk/forum/index.php?topic=63183.msg1470833#msg1470833A Google search for (don't use quotes): Luxos U +regen or +schmutz (rain and filth) will get you more, once translated.
Meanwhile, there can also be issues if the Luxos is used with B&M's Toplight line Plus *brake* light:
http://www.joe-bike.com/2013/06/12/safety-notice-got-both-luxos-u-and-toplight-line-plus-brake-lights-read-this/Hope this helps. Again, I'd ask the vendor and then B&M for suggestions.
Best,
Dan.