yeah, make sure to solder this wire first, on that side too, (+) hold the plug with pliers or something, because it gets really hot when soldering..
put a bit of tin on the plugs, and tin the wires as well.
then heat the wires again, press them against the plug, and put a little bit of tin against it, so it all melts together..
That does the trick..
Make sure the heatshrink is away from the plug when soldering, otherwise it will shrink on a point you dont want it.. ;)