sonett - Installing replacement brake light switch
There Sonett includes a brake light switch directly on the master cylinder. The switch takes the place of one of the banjo bolts. Mine failed, presumably due to exposure to salt water, though this is apparently a common part failure. These switches are not made any more. There are a couple parts that cross reference as compatible but I read mixed reviews from other Sonett owners on how well they work.
I opted instead to use a conversion kit from Mark Ashcraft, kit 4020. This puts the brake light switch at the brake pedal. When you press the pedal, the switch is released thus turning on the brake lights.
Installation was straight forward and it works. Perfect.