Firstly, three way switches can get a bit complicated, and some assumptions are necessary...........although they might not be correct.

With the three way switches, one of the switches will have 115V coming into the box............and the other switch will have the output wire for the device. This must be determined first. If you have a meter, shutoff power to the circuit and find the single wire that goes to the device. It will be on one of the "common" terminals of the switch. On the other switch, this same terminal has the incoming 115V power. You can also verify this, carefully, with the power on...........although I don't recommend it due to safety reasons.

When you have found the incoming 115V wire on one switch, and the output to the device from the second switch, you can now decide where you want the fan control.

The fan control needs the 115V supply wire and it needs the output wire to the fan itself. But, in your case, they are in two different boxes. However, you've now got two extra wires that run between the two switches.........one of them is red..........the other is either black or white. Either one can be used as the connection between the two boxes.

So, to bring 115V to the second box (if necessary), connect the incoming 115V line to one of the other two lines (don't use the red one) to take it to the second box (the box with the wire to the device).

Or, to bring the device to the 115V supply wire, connect the wire to the device to one of the other two lines to bring it back to the box with the 115V supply.

When you get done, one of the three wires will not be connected to anything..........at both ends..........and this should properly be the red wire...........because you are not using the three way capability anymore.

Sorry for the long explanation, but the three way switches are a bit complicated and you DO NOT want to wire all three wires together.

Good luck. Post back if you're confused with it.