A while ago I needed to build something to convert Plant 3D content into Fabrication content. In order to do that I needed to get access to the connector information of a P3D object and some of its basic properties. I decided to make a .Net plugin that exposed lisp functions to separate the data collection from the actual work I needed to do.
I have made that C# project and the DLL I used available here:
https://houseofbim.com/2017/02/20/project-alyobabetous-lisp-plugin-for-plant-3d/
I tried to be as brief as possible, but if anyone manages to do something cool with this let me know. I find the P3D API to be generally painful, but if anyone wants to update the C# to be more useful I'll gladly repost the update if you want to share it.