The wiring is two conductor and is reversable 24 volt in most cases. 120v is not for the vac itself. The wires tuck under a spring loaded screw terminal on the INLET.
Do not remove the screw as you could lose the spring or the terminal pin below it. Wrap your wire at least .75 turn, clockwise around the screw, if your lines are run with 4 color phone wire, I pair them up but if doing so be sure all terminal points are paired the same color throughout the house.
Wen you get to the vac itself , leave an extra 3 feet of wire and coil around a pencil or screwdriver to make a spring ala telephone cord style. This will give you some slack at the wall in case anything hits you wire and you will look like a pro!