FWIW... If a connection between wires can move, I am not a fan of soldering because the soldered connection is so brittle. If you do solder it, encasing it in heatshrink tubing or tape will help immobilize the connection. An alternative is using crimp tubes. As long as the crimp is solid (i.e. you can't tug the wire out of the tube) and the crimp isn't at the very end of the tube, you get a solid connection that handles flexing better (it has a sort-of stress reliever in the section of tube before or behind the crimp).