What are the odds; you have to think. So I'd be at that oil tank and watch the return line disrupting that pool of oil. I would not even look at anything else but that hole times finger off the button and count those seconds off. Not a ripple within seconds say, it's not the washing. Get it?
That, or the drop is making contact to ground. Key on, the mechanical touch points make contact to ground so light is on with key on. Start the bike, the oil's pressure overrides the spring that pushed to make ground is now off the contact point; light goes off, right? Make sense?
Bad, I'm going to use your bike as an example. This is more like an oil thread in a way. Where you are the wash argument and I am the wipe argument. This is more or less a cheap seated computer bike needing a weatherpac. This is not a car about to see all weather and ride in the slush kind of bike. My computer bike is weatherpac'd, but I wipe it down with WD-40. Everything but the rubber and seat. Chain uses grease but that's a different argument v. WD.
My way of looking at the right switch alone, and that exposed mini-motherboard: just imagine if I laid down my computer tower and poured water over the soldered side that now sits horizontal. WATT do you think might happen? And that is why I would not wash a BD just for that reason, let alone the rust forming you can't see.
Signed,
Show bikes show no rust