The brake switch is connected to both the seat switch & the lap bars
2 individual circuits
The first one prevents you driving away with the parking brake on as it destroys the brake or on drum brake can cause the mower to flip
The second circuit prevent the mower running away if you fall off .
This is of course generic information
For specific information about YOUR mower we need to know exactly what it is and that means you need to post the model & serial number off the id ta.
Husqvarna put the wiring diagrams in their parts book and the parts book is a free download from Husqvarna.