I have one wire run into my bathroom ceiling and I want to replace an existing fan with a light/fan combo. I only have 2 weeks wires, one black and one white. My new light/fan combo requires 3 but it would be very difficult to run another wire. Can I splice my current hot wire into 2 and use one for the fan and one for the light?
Or, probably a better solution, you can simply join the fan, power, and light wires all together in a single wire nut (3 nuts: black, white, green/bare copper). To be clear: this will result in your light and your fan always being on or off together.
However, if you can possibly run another set of wires (typically a set of 12/2 or 14/2 "Romex" - a black, a white, and a bare copper wire bundled into a plastic sheath) from the switch to the junction box for the fan/light, I would encourage you to do so. They sell duplex switches that will put two switches into a one-gang box, so you can separately control the lights and the fan.