Honeywell RTH6500WF User Manual page 19

Installing your thermostat
Alternate wiring key (conventional system)
Do not use K terminal. For future use.
1
If your old thermostat had both R and RH wires, remove metal jumper.
2
Connect the R wire to the RC terminal, and the RH wire to the R terminal.
Remove metal jumper connecting R and RC only if you must connect both
3
R and RC.
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