Do you have free-play at the brake pedal?

You need about 3/8" so the master cylinder port will unmask and allow make-up fluid in.


Fwiw, if you're using silicon brake fluid it will creep past the internal seal and get into the switch insulating one side from the other.

When new, the hydraulic switch operates the brake lights with very little pressure.
If it takes more and more pressure at the pedal to operate the brake lights thats a sign the switch is leaking internally.

Mechanical switches aren't difficult to install.
Just need a little imagination.

The one I installed 14 years ago is still as sensitive as it ever was.