APC such as Chemical guys all clean or OTC cleaner use with brushes to get into cracks and crevasses. When rinsing use little water as possible. Cover sensitive areas such as Batt, Alt, MAF, plugs. As for shine I recommend using Chemical Guys VRP or CG's Black on black. The reason I am saying chemical guys products, because they go further than OTC products. OTC product from Walmart or AZ or anywhere will give you a cheap looking shine that isn't durable.
I used Super Clean that you can get from Autozone...
I unplugged and removed as much wiring/parts as I could without getting too involved, sprayed it on the fender aprons, firewall, etc. and scrubbed it by hand with a brush. Rinsed it off with water, I was shocked by the difference.
I just use some cheaper degreaser and some water and a soft brissle brush. I worked at a GM dealership for 2 years as a mechanic and they used to take power washer and open hood and go to town. There was 1 time where I worked on a 08 zo6 and they did this and shorted the fuse block and the horn was stuck blaring on, quite embarrassing and made for a real angry customer so I would be careful. I usually just take a plastic shopping bag and cover my intake filter element. Then simply be careful the battery can get wet and all the electronics can but the biggest thing is to let it air dry or dry with compressed air and let sit before you drive the vehicle or do anything. Nice thing is the mustang fuse block is out of the way and you could simply wipe with back to black or something like that but I would be careful about ignition coils and stuff like that.
I use "Awsome" you can find it at most dollar stores. It is an all natural degreaser that does not damage things like stickers, but does breakdown even the baked on grime. Tip disconnect the negative battery cable and wrap a plastic bag around the cable end before rinsing down the motor and DO NOT spray directly at sensitive electronic components. Mix up a table spoon of baking soda and a quart of water in a spray bottle and spray down the battery before you degrease the engine and when you rinse, the battery will come nice and clean. let the engine bay dry for a good while before replacing the negative battery cable and starting the car.
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