Adding a tower beacon just takes 4 steps:
1) save the beacon template file below into your \scenery\places\(airport) folder where the (airport).tsc file is located and name it "(airport)-beacon.toc"
2) edit the first line to match your airport / file name you just saved
3) copy your airport tower lonlat coordinates from your airport tsc file and paste them into the position lines on rows 6 & 13 of the new file
NOTE - you may have to adjust the height of the 2 lights if your tower is taller than 15 meters (increase the "15" after the lonlat numbers)
4) add a new toc section to the end of your airport's tsc file and reference your new beacon.toc file