Usually there are just four thermostat wires coming from the furnace. Red, White, Green and yellow. Older houses used 2 wires (no AC). Casper is correct, make sure you mark the wires you take off the old t stat. By the screws there should be letters-B or Y or W or G. Just re attach the wires to the like marked screws (terminals) on the new T stat. EZ as 1-2-3.