Let's try a new approach here: What colors are your wires? The indusrty standard is a black, a blue and a white wire coming from the engine. The CDI, which is the small black plastic box typically has a black and blue wire coming from it along with the larger diameter lead which is the spark plug wire. It will be black also
The kill switch has two wires that could be yellow and green, red and black or green and red, or some other combination of colors. The wire colors are not important because the kill switch is just a simple normally open contact that connects the two wires coming from it as noted on the diagram. Those two wires, whatever color they are, should be connected to the blue and black wires that you'll need to connect from the engine and from the CDI (coil). Please forget about the wire colors and try to follow the wiring diagram that I posted for you. Also disregard the "optional method" dotted lines on the diagram. Let me know if my explanation didn't clear this up for you.
As far as the printed instructions; they are often translated into English by the Chinese factories that produce the engine kits. There are often mistakes and inconsistancies in the instruction sheets. We call it Chinglish. Have you ever tried to assemble a tool/lawn furniture/toy that was manufactured in China and had trouble reading the instructions? Same thing here. As you said, they tell you to ground (earth) the wires from the kill switch. That will accomplish nothing and you'll be unable to shut the engine off with the kill switch wired as your instructions say.
Tom