Microphone, Handsfree Malfunctioning

Microphone, Handsfree Malfunctioning:

Fault symptoms
Microphone does not work.

Fault diagnosis
Note that the microphone has a high-level and a low-level output. Connecting the wrong microphone output can overdrive the unit or give too low a signal level.

Check the wiring harness
Jiggle the wiring harness at several points and in different directions to reveal intermittent breaks and short-circuits in the leads.
Observe the multimeter, test lamp or diagnostic instrument during the test.