Honda BIG RED 2009 Owner's Manual page 114

4. Remove the reserve tank cap.
Always add coolant to the reserve tank. Do not attempt to add coolant
by removing the radiator cap.
UNDER FRONT HOOD
RIGHT FRONT
5. Add coolant to the reserve tank as required to bring the coolant level
to the MAX level mark.
6. After adding coolant, install the reserve tank cap and close the front
hood.
Coolant
reserve tank cap
Servicing Your Honda 105