Want to replace with honeywell rth7500. This is what I have ciphered so. I am trying to replace my trane weathertron emergency and aux heat thermostat with a Honeywell RTH7500. The wires I have are R, T, O, G, Y, X2, B, U, W, F. After looking at the installation instructions I was able to cipher: R - R O - O/B T - I dont know G - Green Y - Yellow X2 - E B - C U - I don't know/ I think u & w connect together W - Aux F- Nothing Can you please tell me what to do with T and U. I think the rest is correct. I can be reached at (205) 752-4321 James Shamlee