One front headlight came on while sitting with engine off

[mattn]

Looked outside after a rainstorm and the driver’s side headlight of our 2010 Mini Cooper was on. The car had been sitting with the engine off for several hours when we noticed the light. We went out, started the engine and turned the lights and off. The lights went off and remained off.

It was after a hard rain and the car has had some water leaks in the past in rainstorms. So I suspect water of course, but any idea what exactly the water go to in order to make the light come on?

Thanks