(external) kernal replacement works only works on C64s (because of the way this is achieved on the expansion port), on C128 you can only use function ROMs.
Ahhhh. I did not know that
... No problem. I will just use another fastloader or maybe even buy a couple of original JiffyDOS roms ... 
When the kernal entries are green this means that the wire to pin 28 has been detected, and it should work if the Sidekick64 works properly (did you build it yourself or get it prebuilt?). Have you double-checked filenames and paths?
I am more or less sure my SideKick64 works as it should. I bought an .42 version PCB with the SMD components allready soldered from Restore Store so I only had to solder the pin header, screen and some pins. I think I did that correctly.
As far as I can tell, all the functions I have tried works on my C128 - except kernal replacement. Playing SID's, loading CRTs, direct load of .PRG files, 8 SID's emulation. The only "issue" I have is that sometimes (once in every 5/10 cold boot) the menu does not come up when I start. However, that is taken care of by pressing the right most button a couple of seconds.
Even if the device work I am, however, not sure that I know how to use it properly .. learning that. And any pointers to guides etc. would be highly appreciated.
Thank you for the reply and a cool project 