Pinpoint Test D: The Audio System Illumination Is Inoperative

D1 CHECK THE VOLTAGE TO THE AUDIO UNIT
- Key in OFF position.
- Disconnect: Audio Unit C290a.
- Place the headlamp switch in the ON position.
- Rotate the panel dimmer switch to the full illumination position.
- Measure the voltage between the audio unit C290a pin 1, circuit 19 (LB/RD), harness side and ground.
  
  Fig 1: Measuring Voltage Between Audio Unit C290A Pin 1, Circuit 19 (LB/RD), 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 THE GROUND TO THE AUDIO UNIT
- Place the headlamp switch in the OFF position.
- Measure the resistance between the audio unit C290a pin 2, circuit 57 (BK), harness side and ground.
  
  Fig 2: Measuring Resistance Between Audio Unit C290A Pin 2, Circuit 57 (BK), Harness Side And Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : SEND the audio unit to an authorized repair facility. TEST the system for normal operation.
- No : REPAIR the circuit. TEST the system for normal operation.