All of our bathrooms have the vanity light fixture and the ceiling exhaust fan connected to one switch, so we can never just have the light or just the fan on. They are ALWAYS on together. We want to put them on sperate switches, but when we opened the face plate we found to white wires bound together with a cap and 2 black wires one going into each side of the switch, plus the grounds. Through trail and error we found one Black and one White were live wires, we tried multiple combinations but can't seem to get the fixtures to separate. Is it even possible? I am wondering if maybe the light and fan connect somewhere in the ceiling. I clearly have no clue and would appreciate any input out there. Thanks :)

You have black and white for power in, the other black and white goes to light then fan(or vice versa)If in conduit or if you can get another conductor to first fixture, then you could use combination switch, open to 2 gang and have separate switches, Or a couple of manufacturers make super silent exhaust fans, you have to listen careful to hear, Bad ducting can make it louder.

Before you continue along with switch analysis, you need to make sure that your fixture will allow the switching to two circuits.

If the light and fan are wired together, then you may not be able to separate the circuits.

Also, given the type of connections you describe, you should never find voltage on the neutral (white) wire. However, if you put a meter between a black and white wire and you read 120 VAC, then you have found the primary feed line.

Black is hot and white is return or Neutral. What you are reading is the difference between the two poles.

Regardless, the primary black should go to the bottom screw screw on the switch. This is the line in. The top of the switch is the Line out. Line voltage is carried only on Black or Red wires. However, if there is a white wire with black tape on it, it's telling you that that particular wire is used to carry line voltage, not Neutral.

Also, three white wires capped off with a wire nut is called a pig tail. You want the Primary 's white and to White to the light tied together in the pigtail. That should get you back to working as designed.

To split the switches, you would need to pig tail the Source feed to both switches. You would connect the main Black to a Black got to the Line IN on one switch and another black lead to the Line in to the second switch. Finally, you would add the White to the white wires under the cap to create a second pigtail.

You will also have to add a "Double Gang" box where the original switch was and run a second line up to the fixture for connection to either the fan or light. S1 would service the other need. And then a new double holed faceplate to cover the gang box and allow an opening for each switch

More then likely you will need to pull an electrical permit to do what you want to do, which also means that you have to sketch out your circuit design and show it to an inspector when you apply for the permit. When the work is done, the inspector will come out and verify that it is correct.

If you don't have the work inspected and approved, then you have just opened and enormous hole in your insurance coverage if there should be a fire.

It sounds like there is probably only one hot lead going between the switch and fan and you will not be able to separate without running an additional wire.