Pollak 21-478 Precision Ball Switch – Normally Closed (N.C.) – Fits Weather Pack (WP) 12010973

The Pollak 21-478 Precision Ball Switch is a heavy-duty, Single Pole Single Throw (SPST) Normally Closed (N.C.) sensor designed for vehicles operating in extreme moisture, dust, and vibration. This switch features sealed terminals specifically engineered to mate with the Weather Pack (WP) 12010973 connector, providing a watertight and corrosion-proof connection essential for under-chassis and engine-bay mounting.

Unlike standard backup switches, the 21-478 functions in a Normally Closed state, meaning the electrical circuit remains "On" until the ball is mechanically depressed, which then breaks the circuit (Off). This makes it the ideal choice for door-ajar sensors, compartment lighting, and safety interlocks where you need a signal to activate upon the release of a mechanical trigger.

Built with a rugged, zinc-plated metal body, the 21-478 is designed to resist road salt, grease, and grime. Pollak’s precision-ground ball technology ensures smooth actuation and consistent electrical contact over thousands of cycles, making it a reliable component for heavy-duty trucks, agricultural equipment, and construction machinery.

Common Applications:

• Compartment & Tool Box Lighting: Automatically turns lights on when a lid or door is opened.

• Door-Ajar Indicators: Alerts the operator when service or cab doors are opened.

• Safety Interlocks: Monitors the position of guards or levers to ensure safe machine operation.

• Industrial Limit Switching: Provides reliable position sensing for heavy equipment components.