When a switch is removed from a circuit, what diagnostic test is recommended?

• A. Check resistance
• B. Check voltage
• C. Check current
• D. Check capacitance

Answer: (A)

When a switch is taken out of a circuit, the most informative diagnostic step is to check resistance. This measures continuity between the points the switch would connect and reveals whether there’s an open path or an unintended short elsewhere in the wiring. With power off, an ohmmeter applies a small current and shows how easily current would flow if the switch were closed. If the resistance is very high or infinite, the path is open, indicating a break somewhere in the circuit. If the resistance is near zero, there’s a direct, unintended connection or a path that would allow current to flow when the switch is closed. Voltage and current tests aren’t as useful here because there’s no complete circuit when the switch is removed, so you wouldn’t get meaningful readings. Resistance testing directly confirms the integrity of the path and helps isolate the problem.