All bikes with ABS have the grey wire for abs diagnostics. At least it's in all the service manuals. You ground it and it puts the ABS controller in debug mode. The ABS controller is a bit like the ECU, a little computer with inputs and outputs so it has diagnostic codes to indicate what's going on.
2018 Ninja w/bags, Motowerks lowered pegs, Sargent Seat, Puig/Vstream screen, Givi XS307 tank bag, WOLO BadBoy horn, Aerostitch Roadcrafter