I have the VN900 Service Manual, from Kawasaki, but it's the big paper book, so I can't link it, sorry.
The "Front Accessory Connectors", in the headlight housing are marked as being White/Black (power) and Black/Yellow (Ground). They mirror the "Rear Accessory Connectors". The White/Black go through the accessory fuse to Red, which is listed as unconnected in the Off position of the ignition switch. Not sure I trust that, though.
On the other hand, the headlight has three wires:
Red/Black - used all over the place, probably 'running positive'
Black /Yellow - always listed as ground
Red/Yellow - goes to the dimmer switch on the left handlebar, probably 'high beams'
I'd check with a multimeter to be sure, but I think you want Red/Black and Black/Yellow. Might want to look for same-colored wires in the tail, though. The headlamp draws a lot of power.