I stopped soldering connectors in my race cars after a few broke off right outside of the connector; as noted, the solder will tend to wick out into the wire strands, and create a stiff area right there near the end of the wicked solder. All the weight of the wire under vibration will concentrate there and tend to anneal over a period of time, and then break. If you do solder, then it is wise to make sure the wires are well supported a few inches beyond the solder point.
