As a show car fanatic, I hose down engines regularly...the tips by those who previously posted are proven, and they work!
High-pressure can also force water into crevices that would not normally be introduced to water...so beware! If it was hard to get water there in the first place, it will take awhile for it to be expelled! So if you MUST use the car wash hoses, use the "engine clean" cycle at low pressure only.
MB wisely placed the sensitive electronic controls in protected bunkers away from the areas that would most likely see water...so that is a good rule of thumb to use when you do put the hose to the engine...in other words, don't hose off the battery compartment!!
Sometimes getting water on ignition components can be unavoidable...and that's ok. Just make sure you get a towel and blot off the excess moisture on both electrical and mechanical parts, especially in places where water can pool for days before evaporating...spark plug holes make great moats in some engine configurations.
Note that after a thorough washing, exposed lubricated parts have probably had much of their lubricant washed off. I usually go and relube those components after I'm finished.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car