The exe.xml file Michael refers to must be in the correct directory (tells the flight sim what addons to launch)
For Prepar3D v3 it looks in
C:\users\<yourusename>\AppData\Roaming\Lockheed Martin\Prepar3D V3
The new SaiFlightSimX.exe "Plugin" is now an integrated support plugin (BTW it is the same code for FSX, P3D v2, and v3) which combines the support for Instrument Panels and the other Saitek Radio/Multi/Switch panels ---- will probably conflict with SPAD if you have that installed