Ohm’s Law states that the voltage and current flowing through a wire are related to the resistance offered to the current. As resistance increases either the voltage or the current must change. The connections between wires are often the source of unwanted resistance that reduces the available voltage, and this is a particular problem when the voltage is already low. Consequently, poor connections should be avoided. The best connection between two, three or more low-voltage cables is produced by a perfectly soldered joint, something anyone can achieve with a little practice. Connect three cables in the same way as you would two low-voltage cables.
Strip the insulation from the final 1/2-inch of each cable. Make sure that the exposed metal is shiny and bright. If it isn't, rub it with emery cloth until it gleams.
Switch on a soldering iron or gun, and allow it to reach its operating temperature. Touch the end of a solder rod to the tip of the iron and allow a small ball of molten solder to form on the tip of the iron. Rub the tip of the iron on a damp sponge to smear the molten solder all over the tip of the iron and to remove any debris, oxidized metal and dirt from the iron. This is called tinning, and the result should be an even coating of shiny solder all over the tip of the soldering iron.
Twist the bare ends of the three cables together to create a firm physical connection between them. Tug gently on the wires -- they should remain bound together.
Rest the bare metal end of the combined cables on the tip of the iron. Allow the cable ends to heat up for about five seconds. Touch the end of the solder rod to the top of the cable, not to the tip of the iron, and allow the solder to melt and flow over and through the cable. When the cable end is completely coated in molten solder, remove the soldering iron and allow the joint to cool slowly. Don't blow on it or cool it rapidly.
Wrap the entire joint in electrical insulating tape once it is cool, to protect it from corrosion and damp.