I can't speak to locomotive or aerospace, but I found The Reluctant Motor Mechanic by John Fordham a great introduction to how cars work. It was written in 1979

I can't speak to locomotive or aerospace, but I found The Reluctant Motor Mechanic by John Fordham a great introduction to how cars work. It was written in 1979 and you can pick up a used copy from Amazon for approximately $0.01+shipping. It's a thorough introduction to how the whole car works, written to be understood by actual humans who don't have experience with engineering. He goes through each system, starting with the engine, until he has covered every piece of equipment inside your car. It doesn't take as long as you'd think, either - he's pretty concise. It was written in 1979, so it only covers technology up to that point, but since the car is basically the textbook case of what you can achieve through incremental improvements, it's still pretty relevant. Plus, it's got a lot of good illustrations!