Automotive Service Excellence (ASE) A6 Electrical/Electronic SystemsGeneral Electrical/Electronic System DiagnosisMedium
A client complains that their vehicle's interior lights sometimes flicker or stay on dimly even when all doors are closed. The technician suspects an issue with a door jamb switch. Which type of switch is a typical door jamb switch?
- AMulti-position switch.
- BMomentary contact switch.
- CNormally Open (NO) switch.
- DNormally Closed (NC) switch.
Show answer & explanationAnswer & explanation
Correct answer: D. Normally Closed (NC) switch.
A typical door jamb switch for interior lights is a Normally Closed (NC) switch. When the door is open, the switch plunger is released, closing the circuit to ground and turning on the lights. When the door is closed, the plunger is depressed, opening the circuit (breaking the ground) and turning off the lights. A faulty NC switch that intermittently fails to open would cause the lights to flicker or stay on.
Why the other options are wrong
- A. A multi-position switch has several detents and is not used for simple door open/closed detection.
- B. While it is momentary in a sense, 'Normally Closed' describes its default electrical state.
- C. A Normally Open switch would turn lights on when depressed, which isn't typical for door jamb lights.
Normally Closed (NC) Switch
A switch that is closed (completing a circuit) in its default, unactuated state and opens (breaking the circuit) when actuated.
- Default state: closed circuit.
- Actuated state: open circuit.
- Commonly used where a default 'on' or 'connected' state is desired until interaction.
Memory trick: Door closed, lights off, circuit broken, that's NC's law.