Simply connect the black wire (arrow at top left) to everything that needs power (through the appropriate switches), and make sure your grounds are good............If you want to run a fuse, cut the red wire between the ignition switch and the "dot" where the rectifier red attaches to the "heavy" red wire... install fuse holder and fuse...
To run an electric start, use one "post' of the solenoid as the connection point for the red wires (the "dot" above the rectifier in drawing)...Run the (smaller) Black solenoid wire to the "arrowhead", and the yellow/red stripe wire to a pushbutton that grounds when pushed.....The other solenoid "post" heavy wire goes to the starter motor itself (as originally done).
With only a headlight and taillight to deal with, a single DPDT/ center-off toggle switch will handle it..... Next post will detail the connections for brake , tail, and headlight.....