It is mounted in the space that the bulky license plate light was in originally.
So first I cut the plastic license plate holder in half. I removed the old license plate light portion (on the right), and kept the license plate light portion (on the left).
Then I mounted the LED brake light into this space and wired it to the brake light wire, which I tapped into underneath the seat using a Posi-Tap connector.
To achieve a light for the license plate, I used 2 LED license plate bolt lights from KapscoMoto.com, but just look on ebay for "led license bolt".
They are a pain to wire up however, as the nut to hold them on must go over the wires before they are soldered.
Now at this point I removed the big bulky mud flap since I live in a dry area, so I removed it (big mistake!).
At this point the rear fender looked like this:
The problem is that when I removed the big mud flap this exposed a sharp edge for the rear knobby tire to grab onto.
I fixed this by installing rear fender support arms (see the Rear Fender Support mod), and by putting the mud flap back on, and by buying a better shock!