I have an old Honeywell Chronotherm IV thermostat that I am trying to replace with a Honeywell RTF6580WF wifi thermostat. I have a gas furnace and an air conditioner.
Wiring for Chronotherm IV (wires in all terminals but R):
D G B Y W RC R (with wire in RC and jumper from RC to R)
Note that the 'D' terminal above may actually be an 'O' -- it's not clearly marked.
K Y2 W2 G W C Y R Rc (with R-Rc jumper)
I'm not sure what to do with the old D wire (which might actually be a letter 'O' but its very hard to read) and the B wire, and I don't know which one is my C wire on the old thermostat. I know I need a C wire.