Basically the warning lamp connects to the switch in the brake hydraulic distro block (if you have a dual system) and is in parallel with the switch activated by the emergency brake. So either switch goes to ground when activated. Power for the lamp comes from switched 12V IE "ignition run" or IGN1
The parking brake switch works just like a dome lamp......a simple single terminal switch that grounds when the lever is moved.
So the functional path is ignition switch (ignition run power)---to one side of lamp--through lamp---to parking brake switch---grounded when activated.