Never Spray The Engine Down! Never!!!!
 

I raised up the hood to use one of those degreasers on my engine, then after I slightly sprayed down the engine but didn't have problems till about a week later. I would try to start it and it would rev full power but wouldn't turn over! I was thinking it was the distributor, bad main relay,
starter, fuel pump, etc...

I was RELIEVED it was due to only getting the spark plugs wet! Man was
I relieved!!! For now on I will never in my life hose the engine down, only
use a wet rag or whatever.

I've washed the engine bay, but still I was careful about where the water goes. Here's my personal "rules".

Don't spray when the engine is hot. Warm is OK, like an hour after shutdown.

SparkPlug wells. Avoid those when spraying because they're a PITA to dry out.

Battery caps, brake fluid reservoir, powersteering reservoir. They each have little tiny air vents so you don't want to get water in there. Transmissions even have air vents.

Electrical system (wiring harnesses). Not too paranoid, but don't go nuts with full-pressure spray that works into the wiring & won't dry out.

Air filter (maybe). Some cars have an air intake opening where you can spray water way in & soak the paper filter.

If there's a lot of gunk on the engine, don't spray in a direction that pushes the gunk into your alternator, or other places you don't want it.

I've always sprayed both my Accords' engine bays off at the car wash (wash the outside first, while the engine cools). The spark plug wires should seal pretty good on the valve cover, so water shouldn't get in. Aftermarket wires?

I've pressure washed my engine bays before. However, after I'm done I use a compressor to blow out most of the water afterwards.