Okay,here we go! You can add it by right clicking START,program files , FS9 , Aircraft , then click on the aircraft you want to add yaw damper to. Then click on the white & blue 'aircraft' folder , locate under [autopilot] the line that says 'yaw_damper_gain=0.000000 ' ,change it to 1.000000, then save . This will now allow the switch to work. Some panels/planes do not have a 'yaw_damper_gain' line in the config,but you can add it under the [autopliot] line .
The above file can also be used to change the 'manufacturer' of the plane from 'PROJECT OPENSKY' to 'Boeing' , so all your Boeings line up.
Hope this helps!
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