agreed, WD40 will drive out any water (and lose debris if you flood enough through), but thats about it. If there is any damage on surfaces, it'll be no use.
Thinking about it though (and I hope I'm wrong), I'm a bit concerned you might have a broken piece in there that flapping around, making contact when you press the button, and randomly at other times (is the relay noise ALWAYS there, when the bike is idling?)
I do think you need to at least get the housing apart (the easy bit), and have a good investigate.