Top right SPST switch is normally open switch. Turn this switch ON then OFF and circuit powering light bulb (could be device as fuel pump or sirens,ECT) latches circuit OFF. If you want latched ON connect lamp to upper relay contact above.
To Reset: Open SPST switch at left in battery or ignition circuit then close to reset circuit latch.
Might use magnetic reed switch for top SPST switch if you want switch hidden by plastics panel. Then swipe magnet over hidden switch to activate latch circuit.
