Do you need separate light kit power wiring when installing a ceiling fan?

There are several things you should know before you put that fan up. The box which is installed in your ceiling may or may not be the correct box. After you have removed the light fixture look at the box if it a plastic box do not use it. The weight, motion of the fan will work the screws out and the box is not made to carry that much weight. The hardware stores sell a box and bracket that will work for you, now onto the electrical turn the power off at the breaker you will have to open the splices that are in the box to change out the box. Depending on the wiring of the house it may be possible to add a switch for the light but lets keep it simple for now yes the wires from the switch are used to control both the light and fan. You will have to use the pull chain on the fan as the switch for the light.