The real-world R22 does not have a beacon light, only a strobe, so the aircraft.cfg light fix in the first post is the correct one to use, but it is only halfway there; you also need to change the light fx entry to fx_strobe, as follows.
:light.3 = 2, -18.90, 0.04, 2.58, fx_strobe
This information was verified by a panel image search, reference to the R22 POH, and internal/external video of the real-world R22 startup procedure. Something a "purist" would have done.