A weak connection of the wire to the solder tab or circuit board. A cold solder joint is likely to break off and have high resistance. It is usually a dull gray in color and may be chunky rather than a smooth droplet of solder. A good solder joint will be a shiny silver and be smoothly shaped like a water droplet. A cold solder joint can be the result of a low-wattage soldering iron, such as a 30 watt. Try a 60 watt soldering iron and clean the tip with a damp sponge regularly. You also might consider using flux to tin the surfaces and wires you are soldering.