It's a bit difficult to know what you mean with your question...What kind of loom you do have. A wire scheme for the 101 is quite easy to find on the net. Be aware that 28-30 scheme is showing connections for the quite rare toggle switch on the panel. -31 scheme shows the twist switch more commonly used. You can also find a more detailed panel wire scheme that shows connections for the twist switch.

If I refer to the orig. Indian loom, the green wire is connected from the switch on the panel to the generator +, and a short black wire is going from the generator body to minus on the battery. From the same screw as the green wire on the switch, a red wire is going via the amperemeter to the battery +.

The cut out relay is connected on the generator between the stationary brush close to the + stud and the + stud, so the relay cuts out the brush and + stud when generator is standing still in order to prevent battery draining.

Really, I would alter the generator to a 2 brush system, it is a lot better for both the battery and generator longetivity. When you do that you disconnect and remove the third movable brush and connect a solid state regulator to the field coil and brushes. It is a very small modification and totally reversable.

The 2 brush regulator regulates the current to the field coil based on the battery charging needs, and lamps consumption. The battery will last longer when there is little risk of overcharge and boiling dry, or drained low on power that is equally bad for the battery longitivity. And the generator is running cooler when it doesn't need to charge fully all the time.

You are right, the ground is through the generator body to the bracket, to the frame through the motor bolts to the gearbox and then to the battery. But often there is a lot of paint that hamper the ground, so be sure there is blank spots for good connections. You have the gen firmly screwed to the saddle plate, but be sure there is blank spots for good ground connection. 

For those with the older Scouts with a bracket on the frame tube, it is more troublesome. If it is not desireable to sand off paint on the frame, a  discreet wire to the battery can be squeezed between the gen.housing and the bracket.

The ordinary ground wire goes from the battery to the top cap on the gearbox shifter. But i use to put it under one of the gearbox cover nuts.

Usually the gen. is a DU 5 or 7, a very good repro can be bought here (And some good reading!):

http://www.splitdorfparts.com/

And for identification and spare parts these guys knows far more than me:

http://www.splitdorfreg.com/blancard/splitgenart1.html

http://www.mainelymagnetos.com/MagnetoParts.html