I replaced the old mercury thermostat with a programmable thermostat from Honeywell model# RTH230. The wires on the old thermostat were G, RC jumped to RH, O, Y, W, B. the wires coming through the wall were Red to RC jumped to RH, yellow to Y, Orange to O, Black to B, white to W, Green to G.

The new thermostat was the same but did not have a place for the Orange and Black wire. I googled, and found that the Orange and Black were use for Heat pumps. I decided to give it a go without orange and Black wires connected and it worked!

.... sorta

I notice a huge difference in temperature upstairs and downstairs. It had to be 80 degrees up and struggling for 70 downstairs.

After looking upstairs, my conclusion is that the orange and black wires were routed to the Zone damper (thing). Im not sure what I should do to tap in the extra wires. maybe i need to buy a better thermostat?

Little info about my HVAC that my help...
I have a single unit in a 2 story 1700sq ft house. One thermostat downstairs.

Old thermostat
http://shiftat9k.com/image_gallery/17.JPG

New thermostat and wires
http://shiftat9k.com/image_gallery/19.JPG

Thank you for your help!