The FDR can not recognize the Pmdg’s B738 and B777/B747 aircraft’s strobe light and taxi light actions due to the usage of different OFFSET values which are not belonging to FSX Offsets. (This is a common problem made by Pmdg)

• The first thing that you need to do is to make your Pmdg aircraft start broadcasting it's inner offset values. In order to do that; open the PMDG 737 NGX folder under the main FSX/P3D folder (or open the relevant 777 / 747 folder at the same place for B777 or B747).
• Find the 737NGX_Options.ini file and open it with a notepad editor (Find and open B777 or B747 relevant options.ini file for B777 / B747)
• If this file doesn’t contain the following code lines, just add them at the end :

[SDK]
EnableDataBroadcast=1

• And save this options.ini file. Now your aircraft is broadcasting the necessary offset values.

This is from FSUIPC manual. Use at your own risk !