Thanks for the enlightenment. I noticed that the systems governed seems to be the same for both the K-041 and TNS switches so my guess would also be that it's a backup, but a comment from someone who knows for sure would be great.
I also noticed that in case the K-041 and TNS switches are on, and you turn off either one of them, the navigation system is turned off (ADI, HSI and radar altimeter etc.).