I am trying to install a programmable thermostat (Honeywell RTH6300B) to replace an existing round Honeywell non-programmable thermostat. The wires on the existing thermostat are not labeled and there are only 2 wires attached (green and yellow). There is a red wire that is taped off. The new thermostat has terminals for about 6 different wires, but I am not sure where to put the existing wires. I tried to just match the colors (G and Y) but the thermostat is not responding. Any help would be appreciated.

Without me looking up the terminals and assumin that this is a heating only stat and not one for a mobile home where heat/cool is sselcted at the furnace and a common terminal is not required on the new stat then:

If there is an Rh and Rc then use Rh, otherwise use R on the new stat.

Use W instead of the Y terminial on the new stat.

Post the new terminals or a link to the manual of the new stat.

Perfect! R and W worked. Thanks so much!