An avionics technician is troubleshooting a de-energized, three-conductor wiring harness t… — Armed Services Vocational Aptitude Battery (ASVAB)

An avionics technician is troubleshooting a de-energized, three-conductor wiring harness that is disconnected at both ends. Using a digital multimeter set to the resistance ( $\Omega$ ) mode, the technician records the following measurements:

- Probing between Conductor 1 and Conductor 2 at the near end yields a reading of $0.3\ \Omega$ .
- Probing between Conductor 1 and Conductor 3 at the near end yields a reading of $\text{OL}$ (overload/infinite resistance).
- After placing a temporary jumper wire between Conductor 1 and Conductor 3 at the far end, probing between Conductor 1 and Conductor 3 at the near end continues to read $\text{OL}$ .

Which of the following diagnoses is conclusively supported by these test results?

A
Conductor 1 and Conductor 2 have an open circuit, while Conductor 3 maintains normal end-to-end continuity.
Conductor 1 and Conductor 2 are shorted together, and Conductor 3 has an internal open circuit fault.Answer
C
All conductors are intact, but accurate resistance and continuity readings require the harness to be connected to live operating voltage.
D
Conductor 1 and Conductor 2 demonstrate normal dielectric insulation, whereas the $\text{OL}$ reading indicates zero resistance.

Answer

Conductor 1 and Conductor 2 are shorted together, and Conductor 3 has an internal open circuit fault.

In a de-energized, disconnected harness, isolated conductors should show infinite resistance (

\text{OL}

). The

0.3\ \Omega

reading between Conductor 1 and Conductor 2 indicates an unintended low-resistance connection (short circuit). When a jumper is placed at the far end between Conductor 1 and Conductor 3, a closed loop should be formed with near-zero resistance; the persistent

\text{OL}

display proves the path is broken, confirming an open circuit fault in Conductor 3.

Step-by-Step Solution

Analyze the resistance measurement between disconnected Conductors 1 and 2.

A reading of

0.3\ \Omega

between two wires that should be electrically isolated indicates continuity where none should exist.

Independent conductors in a disconnected harness should exhibit infinite resistance (open circuit). A reading near

0\ \Omega

confirms an insulation breakdown or physical short circuit between Conductors 1 and 2.

Evaluate the loop continuity test between Conductors 1 and 3 with a far-end jumper installed.

The multimeter continues to read

\text{OL}

(overload / infinite resistance).

Jumpering two conductors at the far end forms a continuous loop. If both conductors and the jumper were intact, the near-end resistance should be near zero. A reading of

\text{OL}

indicates that the loop is broken, identifying an open circuit in Conductor 3 (since Conductor 1 is continuous as established in the first test).

Synthesize the two findings into a definitive circuit diagnosis.

Conductors 1 and 2 are shorted together, and Conductor 3 is open.

Both fault conditions are independently verified by standard multimeter resistance and continuity interpretation rules.

Key Concept

Interpreting Multimeter Resistance and Continuity Readings in Wiring Fault Diagnosis

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