Yanmar inition switch Lightings
If I remember the panel from my old boat correctly, the three indicator lights are for the charging circuit, oil pressure, and water temp. When you turn the key on, the charging and oil lights should come on, and go off when you start the engine. If all three are on, even with the key off, I would say that there is most likely an issue with your key switch. That would be the easiest and cheapest place to start I think.