That switch is known as a "normally closed- - - -held open" design. With no outside force applied to the lever arm, the circuit is closed, which sends voltage to either the brake lights or the turn signal switch, depending on whether or not the vehicle has factory-installed signals. When the brake pedal is released the pedal moves the lever to the "open" position and interrupts the circuit. The voltage to the brake light switch is supplied from the same source that provides voltage to the headlights- - - -"upstream" of both switches. If you follow that wire to its source, it comes from the ammeter- - - -"hot" all the time with the ignition on or off. The ground for the tail/brake lights is at the light sockets- - - -at the end of the circuit.

The only vehicles I know of that have switches on the ground side are older British vehicles, and some of the Japanese clones of them.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!