Soldering is really no big deal. All you do is pick up a decent iron, I use a Weller 40w. The lower watt the less heat they put out the longer it takes to heat up. I dont like to wait LOL.  Now the hard part, take the wire you wanna solder and the metal part of the Traxxas plug you want to join. Put them on top of a piece of scrap wood, I got a 1X4 thats 8" long I keep lying around. Put the metal part of the plug down, put the wire on top, there is a line they have on there that you CANT go above or the plastic wont fit. Hold these two piece's together some how. Me I put a metal block on the wire to hold it in place, then with the iron pluged in and hot hold it on top of the wire and let it heat up both the wire and metal plug, hold your wire filler or solder in the other hand and press it against the wire. When the wire heats up enough it will melt the solder into it and onto the plug remove iro and blow on joint to cool down. WAIT BEFORE YOU TOUCH IT!!! It will be HOT, a kind of D'UH, but I still do it every now an then =)~. When it cools down tug on the wire while holding the plug in the other hand, try to pull them apart. if you cant pull them apart you did good. Dont use alot of solder, the more is better rule DOSE NOT apply here LOL. Use just enough to cover the wire.  Here is a good video to show you how to do it, he solders two wires together but just replace a wire with your traxxas plug an you get the idea.
http://www.youtube.com/watch?v=BLfXXRfRIzY