12VAC CT UL Transformer (273-1365) Hints and Tips Faxback Doc. # 34679 Q: What is the function of the three wires? A: The secondary of this unit has two common colors and another color in the middle. The two outside carry the combined voltage output of 12V. By connecting the middle wire with one of the other wires, the voltage is then split in half. (IR-09/23/96)