I just had a Trane XL16I heat pump installed with a XV80 FAU. Right now, the heat pump does not heat the house, but the FAU works on emergency heat. (like i want it to) I noticed a couple of anomilies with the (trane) thermostat wiring. 1) B is not connected to the transformer common on the FAU and thus the thermostat runs constantly on battery power. 2) Y2 is going to BK/Twin on the FAU and then to the heat pump. Its to dark right now to see the wires outside. 3) W1 goes directly to the heat pump as does Y1 and O. Y1 is also connected to Y at the FAU. 4) X2 goes to W1/W2 on the FAU which seems right for emergency heat. Let me know what can/should be moved and a posible wire map for the heat pump as well