Honeywell RTH7400D Owner's Manual page 8

Step 4. Follow Special Instructions (Cont)
4. If you have only one C and/or C1 wire connected to
your old thermostat, connect this wire to C on the
new thermostat.
OLD THERMOSTAT
Y
G
C
69-1726—1
W
R
CONNECT TO THE "C" ON THE
NEW THERMOSTAT
8
LETTER
DESIGNATION
SCREW
TERMINAL
WIRE
WIRE HOLE
M22223