Brake switch is under dash above brake pedal swing arm....if that helps. The are threaded and can be adjusted.
Totally agree that switch is a biatch! I'm guessing your switch may be okay since it was working before the new master cylinder. Does the brake light go off if you physically lift the brake pedal as high as it will go? If so then the switch is working and you just have an adjustment/position issue.
If the switch does work, I'd double check your master cylinder to make sure it is installed/functioning correctly. For some reason your pedal is not being returned enough by the new MC.
If you do need to make an adjustment, you can actually bend the metal plate on the brake pedal that contacts the brake switch enough to make a small adjustment rather than adjusting the switch position (much easier).
Welcome to the site.Odd thing is, no brake lights come on, I have working emergency flashers so the bulbs and wiring going back "should be good". The fuse isn't blown.......I'm befuddled. I'm thinking about using the one cut wire that goes hot when brake pedal pushed and running a new wire back to the brake lights ??? Wish I knew what that wire was supposed to go to......voodoo magic under the dash in wire spaghetti land.