Tacan volume actually works. Cant remember who it was, but he/she pointed out that initially before it has a station tuned in (range and direction showing on HSI), the Tacan volume has no effect. You have to wait for it to be tuned in, range and direction showing, then you can adjust the volume. So it will beep during its warmup phase with no effect of the volume adjust.
Now if the volume should work during warmup?
Beacon, I believe that was in 2.1/1.5, so pre-deferred rendering.