Brake Fluid Pressure Sensor/Switch: Description and Operation

Fig. 3 Pressure Differential Valve & Brake Warning Lamp Switch.:

Fig. 4 Dual Master Cylinder W/Built In Warning Lamp Switch.:

DESCRIPTION
In Fig. 3, as pressure falls in one system, the other system's normal pressure forces the piston to the inoperative side, contacting the switch terminal, causing the warning lamp on the instrument panel to glow.

In Fig. 4 shows the switch mounted directly in the master cylinder assembly. Whenever there is a specified differential pressure, the switch piston will activate the brake failure warning switch and cause the brake warning lamp to glow.