Re: Changing single pole switch to 3-way
You will need to run a new 14-3 from the switch box to the new switch box. Connect the always hot on the old switch to the "C"terminal on the replacement 3 way, connect the white and red wires of the new 14-3 to the "T" terminals on the replacement 3 way, wire nut the switched wire from the old switch to the black wire of the new 14-3. In the new switch box connect the red and white wires to the "T" terminals on the new 3 way, and the black wire on the "C" terminal of the new 3-way.
Be sure you live your life, because you are a long time dead.-Scottish Proverb