This link should give you what you want. See step 3. These instructions also show you which color wire to which color.
http://www.geocities.com/fulltimedre...m_upgrade.html
We made the same change you are making (definitely worthwhile). The "extra" wire is because you have one lead for high speed fan and one for low speed. The new thermostat only uses one wire so you have to choose between high and low speed. Or you can add a separate switch between the two wires, feeding one wire out to the thermostat connection (some have done that). I just left ours set at high speed, which is fine with us. Plus, duotherm air conditioners tend to ice up when on low fan in high humidity situations but not on high speed fan.
If this link is not what you're looking for, please post back.