you had to do the same with FSX although the installer may have handled it automatically
No, it doesn't do it automatically, although the Readme has a how-to section for editing the exe.xml file, to add the appropriate section to make AICarriers start automatically. As may have been mentioned before, always, ALWAYS use NotePad to edit the exe.xml file (.cfg files too!). If you use a word processor it will add symbols to the file that make them unusable for FSX or P3D. You also ALWAYS make a back-up of any file before you edit it.
I don't know about P3D, as I don't have it, but for FSX, the exe.xml is found in C:\Users\YOURUSERNAME\AppData\Roaming\Microsoft\FSX . At least on a Vista machine. Again, the Readme file has a section showing where the exe.xml file is located, for FSX, for the various OS's. I believe it's location is similar for P3D.
When adding the entry to the exe.xml file,
<Launch.Addon>
<Name>AICarriers</Name>
<Disabled>False</Disabled>
<ManualLoad>False</ManualLoad>
<Path>C:\Program Files\Lockheed Martin\AICarriers NET\AICarriers.exe</Path>
</Launch.Addon>
don't neglect the line </Launch.Addon> as the last line of the entry. You didn't show it in your example in your last post, expat. Just a note.
Also, you must dl and install the correct .NET Framework. The correct version, and where to DL it from, are, again, included in the Readme file.
I placed it in the Parent folder of my P3d4 installation (i.e.the "Lockheed Martin" folder)
I've seen entries in the AICarriers forum over on the FSDT site that indicate that AICarriers must be installed within the root P3D folder, as shown, to function in P3D. I've also seen posts on other forums that contradict this. I always recommend installing it under the root P3D folder, just to be safe.
Although all I do is double click the AICarriers.exe once I'm in P3D and it all works.
I made a shortcut to the AICarriers.exe file on my desktop. That way I don't have to dig it up if I need to start it manually. I set the shortcut to start AICarriers as Administrator. Tends to prevent a lot of problems that can occur. Just a suggestion.
Hope all my babbling helps a little...
Pat☺