I moved a three gang box that controls the light/heater/exhaust combo in my bathroom which required me to extend the wiring, I didn't change out the fixture and everything in the breaker box is the same. I thought I did a good job of getting it put back together until I tested my set up. The light works, the exaust works, the heater works... here is the catch. When I have the light on and then turn on the heater as well, the light turns off. I've been reading around on the net and it seems most set-ups have a 12-2(which seems like the feed) and a 12-3 to control the fixture. However, what I have is three 12-2's, the home was built in the early '80 in Texas. On one 12-2 set I have a black wire that runs to the bottom of each of the three switches in a daisy chain fashion, the white is tied to the white of the second 12-2 set, the ground is tied together with the grounds of the other two 12-2 sets. On the second 12-2 set the black goes to the top of switch #1 which controls the exaust. On the third 12-2 set the black goes to the top of switch #3 which controls the light. On the same third 12-2 set the white wire goes to the top of the second switch(which controls the heater) and seems to be what is causing the problem. Is there something easy I am missing here? Can this be solved using a different switch? Or should I just hook up the exaust and the light to work on the same switch, cover up the third gang and be done with it? I hope I explained this correctly. Thanks in advance!

Chances are that you have the white wire that is the neutral going to the fan/light/heater mixed up with the white wire that is a hot to the heater.
You know that the white of the cable 1 is the neutral coming to the box because the black of that cable powers the switches. One of the other two white wires is the neutral going to the fan/light/heater, but which one. The remaining white wire is a hot leg to the heater. You need to insure which white wire is the neutral to the fan/light/heater and which is the hot to the heater.

So if this was the case each function would work individually but not together? Can I use a voltmeter to find the white wire that is "Hot"?

You said that you had to extend wiring. How did you do that? Did you replace all the wiring between the fan/light/heater and the switch box or did you replace the wiring between the breaker and the switch box? How many cables in the fan/light/box? Trying to determine if cable 1 is truly bring power to the switch box or if it is just a switch leg?

Try reversing white wire 2 and 3. Most you can do is trip circuit breaker.