basically that would be the easiest way to find out. You could also prob get a multimeter and test for the ground or the others which will have some current going through them. There is really know difference between that plug you have and a 1/4 jack. the jack basically has two wires and two...
I wonder if each of those changes a different effect? Does your amp have built in effects? You could try just grounding the cables individually and see what happens.
I would also recommend going to ultimate-guitar.com into the forums. There is a guitar building and customization forum and a...