You're correct. The black wire with the white stripe is the ground. Goes to one of the 6 screws holding the sender in on the tank. The brown wire goes to the terminal in the middle.
Now that you're in there, it's very helpful to add another ground wire. C1s need all the help with grounding they can get, especially in the rear. Ever notice that your gas gauge reading jumps up 1/4 tank when you put the brakes or the directionals on? Add a ground wire from where the harness ground wire attaches to somewhere on the frame. What I did was run the wire to follow the gas line out to the frame. Connected it there to the bolt that secures the gas line clip to the frame. Down by the right rear wheel. That way accomplishes 2 things. It's hidden. Didn't have to drill another hole in the frame.