Low Brake Fluid Warning
WARNING: This page is about a different car, the 1988 Buick Riviera and 1988 Buick Reatta. However, it is still accessible from the selected car via links, so may be relevant.
A reed switch and float, inside reservoir, activate and deactivate fluid level sensor. The switch is normally closed and opens the circuit between pins "A" and "B" if brake fluid gets low.