A client complains that their vehicle's interior lights sometimes flicker or stay on dimly when they should be off. The technician suspects a faulty door jamb switch. Using a multimeter, how should the technician test the door jamb switch to confirm it is causing the issue?
- AMeasure voltage across the switch terminals with the door open and closed.
- BMeasure the current draw through the switch with the door open.
- CCheck for continuity between the switch terminal and ground with the door open and closed.
- DPerform a resistance check across the switch terminals with the switch removed.
Show answer & explanationAnswer & explanation
Correct answer: C. Check for continuity between the switch terminal and ground with the door open and closed.
Most door jamb switches for interior lights are momentary switches that complete a ground circuit when the door is open. By checking for continuity to ground with the door open (should show continuity) and then with the door closed (should show open circuit/no continuity), the technician can verify its proper operation. Intermittent flickering suggests a faulty switch that is intermittently making or breaking ground when it shouldn't.
Why the other options are wrong
- A. Measuring voltage across the switch terminals might be part of a full circuit diagnosis, but directly checking continuity to ground is a more direct test of the switch's primary function in this typical setup.
- B. Measuring current draw through the switch would be more complex and less direct than a simple continuity check for this type of switch failure.
- D. A resistance check with the switch removed will only confirm its internal state, not how it functions when installed and interacting with the vehicle's ground circuit. It also won't catch intermittent issues when the switch is wiggled.
Door Jamb Switch (Ground)
A momentary switch, typically located in the door frame, that completes or breaks a ground circuit to control interior lights or other functions when a door is opened or closed.
- Activates with door position.
- Often provides ground signal.
- Prone to intermittent failure.
Memory trick: Door switch: open, it grounds; closed, it's free. Test its ground-making ability.