This project seems really great, it seems that the original project is dead (and wont compile in fact), I hope your fork is alive.
Running this on an Arduino nano I'm unable to get anything else than the flight mode on my Taranis. All other data are zeros ...
The receiver is a D8R-XP.
The APM is a 2.6 with ArduCopter 3.2.1
Since the flight mode works the wiring do not seems to be the problem.
You have one of the most recently updated forks of the original project, so I thought you might still be interested in it.
I've been using the code on an Arduino Mini with an APM plane quite successfully for some while, but having now just updated my Taranis to OpenTX 2.1.3 I've found that many telemetry values are no longer working or read unexpected values.
For instance Temp 1 works and shows Mav mode, VFAS works,Heading works, GPS location works, Fuel works, and I think A1 & A2.
What doesn't work now is Altitude (reads a static number), Current, GPS Speed, GPS Alt (reads 10x too high I think).
Not sure if you use OpenTX 2.1 (which has some very nice telemetry features) but expect to have a few issues when you do if my experience is a guide.
I also use the telemetry on a Pixhawk which now has native FrSky telemetry, and all sensors read fine from that.