I used a brake light switch off of a 1949-1954 Chevrolet. It has a spring loaded arm that is normally on and the brake peddle rod needed a small clamp with an arm to hold the switch off until the peddle is pushed down and then the spring arm closes the switch. There is a brake light switch made for a 1928 that mounts on the middle crossmember and ir is also connected to the brake rod with an arm.

The Filling Station has a universal Brake light switch for Chevrolets. It is part # AL-73 in their online catalog. The Filling Station

You can use many such switches, but I have a faith in the ones having a moving "arm". You clamp it underneath. I think I can get some pictures of the well working arrangement on Solan, within end of this week. Coming back here.

I have made a double connection (to both brake pedals) so the light turns on whenever a brake pedal is used.

I used an early 50's chevrolet pick up brake light switch on my 1919 it has a long arm about two inches long to catch the brake peddle. I made a wood bracket for it and screwed it to the floor board. It works great.
Hutch

Certainly different useful arrangements to mount and get such brake lights to work.

Here is mine:

http://s889.photobucket.com/albums/ac98/solan1916/?action=view&current=solan-carb-brake012.jpg

http://s889.photobucket.com/albums/ac98/solan1916/?action=view&current=solan-carb-brake014.jpg

http://s889.photobucket.com/albums/ac98/solan1916/?action=view&current=solan-carb-brake017.jpg

http://s889.photobucket.com/albums/ac98/solan1916/?action=view&current=solan-carb-brake021.jpg