I am trying to change out my old thermostat which uses a mercury switch to a Honeywell ct2800 programmable thermostat. The old thermostat which is also a Honeywell has just 2 wires connected to it and none of the terminal posts got any letter markings. There is no instructions on the ct2800 on changing out a thermostat with 2 wires. Can anyone tell me which terminals to connect the 2 wires to? I connected the 2 wires to terminal W & G but it didn't work so I disconnected it and used my ohmmeter across remaining terminals to see which terminals gives me a short as I turn temperature 10 degrees above room temperature. None of the terminals went from open to short as the temperature was increase 10 degrees above room temperature.

R and W is all you need, it doesn't matter which wire is where.