If the vehicle has several turrets, they are selected incorrectly when installing the pylon.
In the video. The helicopter has two turrets. If you select a shooter, this will change to Engineer 1 when you click OK. And vice versa.
[[ https://www.youtube.com/watch?v=-eKHGqRSh7E&feature=youtu.be | https://www.youtube.com/watch?v=-eKHGqRSh7E&feature=youtu.be]]