Replacing existing ceiling fan, with on/off switch only to wall mount control of light/fan

Question

My old ceiling fan switch used black, red, green (ground) no white. Built after 2004 white was in outlet box, 4 white wires but all together in single cap - not used. New wall mount switch has separate fan on/off, and light on/off - wires are black, red green ( ground) and white ( assume neutral). There is an adjacent wall light switch in the box that uses black, red, green - no white. So, I am guessing I need to access the whites for my new fan. When I first wired I capped one of the 4 whites to my new switch - the other light switch would not power on . I put the borrowed white back to the 4 wires capped together and the second switch worked. I am unable to test the fan until I wire the new fan from ceiling. I would like to make sure the wall switch is functioning before I get the ceiling fan wired in place.

So, how do I wire the new switch with the existing scenario ? Which of the 4 bundled white wires do I use, or do I wire my white wire from the new switch to the 4 bundled white wires? Please Help!

Answer 1

To just answer your question, you need to attach your switch white wire to the bundle of white wire. You never, never want to separate the white bundled neutral wires and then energize the circuit unless you really know what you're doing... like as a professional.

Be sure to turn off your breaker before doing any of this wiring.

If you include pictures of the box and switches, we can help you further.