I am wanting to replace my old theromstat with a programmable theromstat. However, I have run into a slight issue. The old thermostat only has two wires coming out of the wall and three wires ( yellow, red, white) tied to the mercury. The one white wire is going back into a radial button that states longer on it and some numbers. The two wires that are coming out of the wall that are tied to screws are red and yellow. Looks like the red is R and the yellow is W. Then it looks like they are tied back to the mercury but because of the radial button I cant see behind where the three wires going into the mercury are coming from. Also, another point the two wires tied to screws aren't really lined up with the letters. The letter W is all way to the top and the red is going into a screw cap that's close to the W, but not like the manual shows. Same with the yellow. I am trying to remove the old thermostat and install a Honeywell programmable thermostat. Any suggestions from anyone would be beneifical?

Thanks