I think maybe he meant
HornetFCS.dll, but I may be wrong.
As long as it's in the plane's Panel folder it'll work fine, but if you put it in the sim's ...\Gauges folder more than a single plane can use it.
For it to work, though, the correct C++ Redistributable must be installed, which is what
VC_redist.x86.exe in the
Redist Update folder, in the v17.1 zip file, is designed to do. The v16.1 iinstaller should do it automatically. As long as you ran that, the HornetFCS.dll SHOULD function correctly. If you do NOT get a FCS Failure message in a green bar across the screen, and/or on the HUD, when you first load the plane in, that isn't the problem, i don't think...
Is your default flight, by any chance a cold-n-dark set-up? That can cause problems like this. If it is, try setting your default flight to the original default flight the sim came with. A quick, easy, way to do that, as you may know, is in the (for FSX, I presume P3D has a similar file) FSX.cfg file, under the [USERINTERFACE] heading, in the line SITUATION= simply delete anything after the "=" sign, the restart the sim. That's just a thought, though.
You did check, I presume, that the Battery and two Generator switches were all on. That could cause what you're seeing, if they aren't.
I'm just throwing out anything I can think of, in the hopes something will stick
Pat☺