Off. Cool. Stay away from the Power Distribution Box. Dont drown the alternator (a little water wont hurt it, just dont flood it). Low/Med Pressure. Thats it.
I'v been washing mine that way for years.. works great. In your manual there is a diagram of what not to soak, might want to review that just for good measure. Dont use harsh chemicles, Orange Clean or Simple Green work best.