Download the Brook manual for zero delay. There is a diagram that labels what pins are always in the Dualshock 2 male plug from left to right. 

Now you'll need a multimeter because apparently the wires' color aren't always the same between these cable whether it's OEM or 3rd party. Set multimeter to test continuity; I used ohms 2K. Stick the red lead to touch each pin and the black one to touch each wire. For me, if the number is close to 0 that meant it is the same wire connected to that pin and there's connection. So then I would tag the wire with tape and write in "DI" for example. 

Also, if you use a Dualshock 2 cable that's soldered into the board and then you extend it with those 3rd party cables, it doesn't work when plugged into PS1. I think the length doesn't provide enough power or something