The engineers go to a lot of work making sure the engine is pretty secure. When you wash your engine, you don't have to cover all the electrical gear.
If you did, there would not be anything left to wash. The only thing you really need to worry about is getting water in the intake. That being said,
dipping the engine in the water won't be a problem as long as the intake is dry.

Did you see the movie "Dante's Peak" he turned his truck into a submarine and drove out of the water. And it emerged completely dry. Ok i know it is a movie...