Honeywell RTH8500 Guide D'installation page 13

Alternate wiring (conventional systems)
If labels do not match terminals, connect
wires as shown here (see notes, below).
Remove metal jumper connecting R and
Rc only if you must connect both R and
Rc wires.
If your old thermostat had both R and
RH wires, remove metal jumper. Connect
the R wire to the Rc terminal, and the
RH wire to the R terminal.
If your old thermostat had only 1 C or
C1 wire, connect it to the C terminal. If
your old thermostat had 2 C or C1 wires,
wrap each separately with electrical tape
and do not connect them.
RC
R
W
Y
G
C
Y2
W2

RTH8500
Rc
2
R
2
W
Y
G
C
3
Y2
W2