Now that we have all of that out of the way, here's what you need to do if you plan to splice a radio slave cable into the MC-25 (recommended if you can afford it, as the strength of a splice is a lot stronger then that wimpy little screw into plastic).
1: Cut off every cord except for the red, purple and yellow ones.
2: Splice the red and purple cables to one of the two in the slave cord.
3: Splice the yellow cable to the other remaining cable of the slave cord.
4: Make sure you protect the splices with a little electrical tape, as well as making sure the other seven wires are covered.
5: Lastly wrap everything up in electrical tape. I suggest making the cable into an "S" shape with the splice in the center, and then tape everything up. That way you help add strength.
Make sense? Good, I hope everything works out correctly. Happy shootin.' Questions can be sent my way.