I had a similar problem after heavy rain. Engine management light and oil light on with out the ignition key. I have even had the analogue clock hands spinning backwards like a windmill. I have even had this idiot light problem when riding in torrential rain. It is water getting where it shouldn't. I regularly lift the tank and spray the wiring loom and ignition switch with WD40 or some other water repellent electrically safe spray. It has sorted it. I still mean to pull all the block connectors on the loom and grease them but that's another day.