As I posted earlier, I just purchased the latest version of the Navigator IV.
I found the display screen very, very dim and suffering from debilitating glare. I called my dealer who told me to increase the brightness using the tool menu.
With the Navigator IV installed in the K1600, it is turned on, go into tools>Display>Brightness. The unit showed brightness setting at '10' (out of 100). There is a (-) button and a (+) button. I pressed the plus button but nothing happened. I pressed the minus button and nothing happened. I checked some other screens elsewhere and everything worked fine but the DISPLAY menu never functioned at all. I started the engine and tried the routine again: same results of inactive buttons in the DISPLAY menu.
I called the dealer and conveyed the problem status. I was told to bring it on in for either a correction or swapping it out for a new one. At the dealer, they tried the identical unit to mine that they had available. To their amazement, their Navigator IV failed to work in the DISPLAY menu and showed only a '10' brightness setting, just as mine did! We next tried mine and they verified the same identical condition. The entire crew at the dealer tried to figure out what was happening but no one could figure this conundrum out. They decided to contact BMW directly on Monday.
I will post an update when I learn further details. BTW, if you hand hold the Navigator IV so that it runs on its internal battery, the DISPLAY setting works properly and can be set to any brightness. But when it is plugged in and mounted in the bike (any K1600 bike), it fails to work.
If anyone else has figured this condition out, please post.