Step #2.)
You need to power your light and switch.
I wanted bright, and old school. So I went with a 12v auto bulb. I may end up converting to a 12v LED cluster later on, but we'll see.
Unfortunately Radio Shack did not carry any 12v AA size batteries like I was hoping to use. They are small, and last quite a while. Instead I went with eight AA batteries, and piggy backed them to achieve the 12 volts desired.
Also available at Radio Shack are the battery holders with the wire leads for about $2.00 a piece. Now that I have power, and leads, I need a box to contain them. You could simply mount the battery holders to wherever on the seat pan as they do have screw mounts. However, one good bump and you have eight AA batteries spilling out all over the road. Also, no working brake light.
As I was building this mod in the kitchen (to much dismay of the SO), I noticed a Tupperware bowl seemed like the perfect candidate for a battery box. Just needed some paint, and a port for wiring. A few screws later to attach to the seat pan, and BAM!!!
The light mount was simple. Two wood screws. If you followed my previous seat pan build, you will know that my nana seat is made from an old skateboard, some carpet padding memory foam, and some poorly stretched leather. So anything attached to it is a matter of some short wood or sheet metal screws.
After mounting, the wiring is pretty simple. Hot wire from battery to first lead on switch. Second wire from second lead on switch to hot wire on light. Ground wire from batteries to the metal casing on the light fixture.
Now you have a working brake lamp.
On my bike it's a little different. I ride. I never idle. If I am on my bike, it is in motion. Therefore I chose a clutch lever with no locking mechanism. My front brake is a hydraulic disc brake. This mod will not work on that particular lever. So..... Under my current riding philosophy, if I am squeezing the clutch, I am slowing down (braking). So this mod went on my clutch lever.
Yes, I have an interesting bike indeed!