Making 3d 'Clickspots'


I am making a 3d simulator and want to add clickspots to my vehicles. EG: User is in 3D train cab and hovers over a certain area of the cab in 3D space and clicks, then something happens. Making a model with visible switches is not a problem for me but actually working out how to register the click in a 3D space is way beyond me.

Thanks for the help,