I had the same issue and after much exploring I discovered just a tiny bit of corrosion in the switch. To repair, remove the squegee section, and water bottle, so you just have the base unit. Then remove the bottom plastic cover and unfasten all the screws. Now remove the switch. With a fine Exacto knife and a magnifyer remove the switch and open it. Check it for corrosion this is whats causing it to stay on. Carefully scrape out the corrosion with the Exacto tool and then carefully reassemble. The light should switch off. You can also test it before reassembly just to make sure all the corrosion is gone.
Because the switch is broken and stuck in the "on" position. Until you fix it all you can do is plug it in and out for operation. If you are handy you can take the switch out, make the repair of the broken part, and reuse.
They wanted 35 dollars for the switch on my Karcher power washer. Yeah, right!
Hi there, if it's anything like my WV50 - which we use for the shower - you'll find that it clogs up after some time and needs to be cleaned out. I've created a video that shows you how to open the head of the unit and clean out any obstructions.
In our case as we use it for the shower, it tends to get clogged with hair, shampoo and conditioner. You may well find that as you use yours for floors that there is also a similar problem.
You need a new battery. I could describe how to rebuild the old one if you are so inclined to do that type of thing. It would save you some money over buying a new one. It looks like it is a specialized piece of cleaning equipment and buying a replacement battery would be fairly expensive.