what to cover when cleaning engine?

ok so ive looked around and got a general idea of good ways to clean the engine bay and most include sprayin it down with water but not too much is said on what to cover if anything at all (electrical etc) is there anything you def must or should cover when you wash down your engine bay with water? tha for the help in advanced

 

I have washed it down numerous times without covering anything. I have never had a problem.

 

ive never covered anything, but i dont have the hose on like full pressure and just attack my engine, i keep it on the mist spray and go over it and get everything pretty damp rather than soaked and just go from there

 

i usually keep the engine running also n fog everything thing down, chill it out, then crank up the power n blast wat mud is left