I purchase a Hopkins Wiring Kit(4pin). It specifies:
Wiring kit Vehicle side
Green Dark Green
Yellow Yellow
Brown Brown

However, when I open the wire wrap, the colors for all four wires seemed faded. There are two "dark green/black" wires. I am guessing one is dark green and one is black. There are also two wires looked brownish. one should be yellow and one should be brown but it's very difficult to tell.

There are four letters A, B, C, D on the connector. Will that tell which line is which?

 

I guess I didn't know what I was doing. I was trying to break a set of wires that lead to the light. There are actually a set of wires reserved for additional lights. I used those and everything works fine.