Good question, my bike is currently apart for farkling so the easy way of answering this question is out
So this is going to be a long nonanswer. Just to make sure that we are on the same page check me on this. There are four connectors for the factory heated grips. The two I pointed out are were the factory grips plug in as temp357 pointed out. There are also two connectors to the control unit. In the first connector, the wire warmachine used connects to the wiring harness, and is R/B in the wiring diagram. This wire is connected to the front cowling wire harness coupler, and according to the diagram of this coupler is connected to another R/B wire. That R/B wire is connected to the black grips connector I pointed out above. The black and gray grip connectors I showed share a common brown/blue wire, and the gray connector is then tied to the windshield drive unit via a brown wire.
The second wire in warmachines connector should be green/blue and is tapped into the headlight relay.
The second connector to the control unit has one grounded wire and a wire that connects to to the ECU. I would guess that this is where the control unit gets speed info from, as the factory units are supposed to be speed sensitive.
The windshield drive unit is a well know source for switched power, the headlight relay I would have to guess is place to tap power that is hot when the bike is running. It would make sense to me that the controller draws power from the headlight relay, and supplies power to the grips via the red/black wire warmachine tapped. So why is the gray connector I pointed out connected to the windshield drive unit? When I originally posted I was concerned that warmachine may have tapped a power source that was not rated for the correct amps for heated grips, he must be laughing his *** off as he cruises around with nice warm hands!