Yes, you can run three conductor cable to five pin connectors, leaving pins 4 and five unused. There are those, that will state that it is not true DMX as defined in the standard. The standard even says that manufactures should run pins four and five from the male to the female connector of the daisy chain loop. It is a lovely thought, but it sure is a lot easier and cheaper to find twisted braid shielded cable in the 110 to 130 ohm impedance. If buget is a factor, which it is for most folks on CB, and you know that you will never use the second pair, then surely run just one pair. Even though several folks have listed the functions on the 3 and 5 pin connectors, it is important to note that the shield of the cable connects from pin one to pin one, and do not connect pin one and the shield to the shell of the connector, the way it is done on some audio connectors. It is important to note that Ground on DMX pin 1 is not the same as chassis ground.