Fluid level warning switch lamp
"What does the brake fluid low warning bulb test do?"
"It prevents you driving along thinking you have fluid when you haven't when really the bulb is blown."
Press the switch - if the light comes on, you know the light works. The sad fact is that typically, in Minis fitted with this bit of kit, the terminals on the master cylinder end have corroded away to nothing, so whilst the bulb works, the fluid level warning system doesn't.
Brake light switch early and late types
Early type
On the older Minis the brake light switch is fitted in the brake line, above the
flexi hose, going to the right front wheel.
Late type
The brake light switch is a 'push to break' type switch and is mounted just
above the pedal arm. As the pedal drops the switch is 'un-pushed' and the
contacts are made, lighting the lights.