I guess I would be looking to see if you have power to the switch after the fuse. Some of the fuse holder contacts fail inside. I repaired one on the road last year. In order for your brake lights to work, certain parts of the switch have to work.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!