I've been cleaning under the hood of every car I've owned since 1974 and gone the gamut on different products and procedures.

Simple Green is a pretty safe biodegradable detergent and makes a wonderful degreaser. It won't turn rubber or plastic gray and rinses clean.

These days I use a 50/50 solution of Simple Green sprayed out of a bottle, wait 5 minutes and rinse with a GARDEN HOSE! 40-50 psig of water is all you EVER want in the vicinity of your engine and it's many triple seal electrical connectors. They (MB) designed these connector boots with the intent of 100-150 MPH air/water mix at atmospheric pressure. NOT a 400 MPH directed spray @ 2,000 psig. I learned this lesson well on my '76 Caprice, one connector leaked, filled up and held water for 2 days until I found it. It was the Throttle Position Sensor and made the car run like it had 5 cylinders until it was dried out. Today's engines and associated electronics are much more prone to problems than in the olden days. No reason to add to it.