Pinpoint Test D: The Audio System Illumination Is Inoperative

WARNING: This page is about a different car, the 2005 Ford Pickup, 2005 Ford F550 Super Duty, 2005 Ford F450 Super Duty, and 2005 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

D1 CHECK CIRCUIT 19 (LB/RD) FOR AN OPEN
- Key in OFF position.
- Disconnect: Audio Unit C290a.
- Place the headlamp switch in the ON position.
- Rotate the instrument panel dimmer switch to the full illumination position.
- Measure the voltage between the audio unit C290a pin 3, circuit 19 (LB/RD), harness side and ground.
  
  Fig 1: Checking Circuit 19 (LB/RD) For Open
  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 57 (BK) FOR AN OPEN
- Place the headlamp switch in the OFF position.
- Measure the resistance between the audio unit C290a pin 4, circuit 57 (BK), harness side and ground.
  
  Fig 2: Checking Circuit 57 (BK) For Open
  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.