Pinpoint Test D: The Audio Unit Illumination Is Inoperative

D1 CHECK CIRCUIT 29S-LK34 (OG/BK) FOR AN OPEN
- Key in OFF position.
- Disconnect: Audio Unit C2188a.
- Place the headlamp switch in the parking lamps ON position.
- Rotate the instrument panel dimmer switch to the full illumination position.
- Measure the voltage between the audio unit C2188a pin 3, circuit 29S-LK34 (OG/BK), harness side and ground.
  
  Fig 1: Measuring Voltage Between Audio Unit C2188A Pin 3, Circuit 29S-LK34 (OG/BK), Harness Side And Ground
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
  - Yes : GO to D2.
  - No : REPAIR the circuit. TEST the system for normal operation.
D2 CHECK CIRCUIT 31-MD34 (BK) FOR AN OPEN
- Turn the headlamp switch to the OFF position.
- Measure the resistance between the audio unit C2188a pin 4, circuit 31-MD34 (BK), harness side and ground.
  
  Fig 2: Measuring Resistance Between Audio Unit C2188A Pin 4, Circuit 31-MD34 (BK), Harness Side And Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
  - Yes : REMOVE the audio unit. REFER to AUDIO UNIT . SEND it to an authorized audio system repair facility. TEST the system for normal operation after the repair.
  - No : REPAIR the circuit. TEST the system for normal operation.