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Pinpoint Test Ac: The Light Bar Is Inoperative/Always On

WARNING: This page is about a different car, the 2006 Mercury Grand Marquis and 2006 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.
  1. AC1 CHECK THE STROBE LIGHTS 
    • Key in ON position.
    • Turn the strobe lamp function on and observe the strobe lamps.
    • Do the strobe lamps operate correctly? 

    Yes  : TURN the strobe lamp function off. GO to AC2.

    No  : GO to PINPOINT TEST AB .

  2. AC2 DETERMINE IF ANY LIGHT BAR LAMP IS ALWAYS ON 
    • Turn all of the light bar functions on and then off and observe the light bar.
    • Are any of the light bar lamps illuminated? 

    Yes  : If multiple light bar functions continue to illuminate, INSTALL a new strobe/light bar control switch. TEST the system for normal operation.

    If a single light bar function continues to illuminate, GO to AC3.

    No  : GO to  AC7.

  3. AC3 CHECK THE SWITCHED POWER CIRCUITRY FOR A SHORT TO VOLTAGE 
    • Key in OFF position.
    • Disconnect: Suspect Light Bar Relay.
    • Key in ON position.
    • Does the light bar lamp continue to illuminate? 

    Yes  : GO to AC4.

    No  : GO to  AC5.

  4. AC4 CHECK THE LIGHT BAR RELAY OUTPUT CIRCUIT FOR A SHORT TO POWER 
    • Key in OFF position.
    • Disconnect: Suspect Light Bar Fuse.
    • Key in ON position.
    • Does the light bar lamp continue to illuminate? 

    Yes  : REPAIR the circuit between the fuse and the light bar. TEST the system for normal operation.

    No  : REPAIR the circuit between the fuse and the relay. TEST the system for normal operation.

  5. AC5 CHECK THE SUSPECT LIGHT BAR RELAY (ALWAYS ON) 
    • Key in OFF position.
    • Carry out the light bar relay component test. Refer to COMPONENT TESTING .
    • Is the light bar relay OK? 

    Yes  : GO to AC6.

    No  : INSTALL a new light bar relay. TEST the system for normal operation.

  6. AC6 CHECK THE LIGHT BAR RELAY CONTROL CIRCUIT FOR A SHORT TO GROUND 
    • Connect: Suspect Light Bar Relay.
    • Disconnect: Strobe/Light Bar Control Switch C3257b.
    • Key in ON position.
    • Does the light bar continue to illuminate? 

    Yes  : REPAIR the circuit between the light bar relay and the strobe/light bar control switch. TEST the system for normal operation.

    No  : INSTALL a new strobe/light bar control switch. TEST the system for normal operation.

  7. AC7 CHECK THE SUSPECT LIGHT BAR RELAY (INOPERATIVE) 
    • Key in OFF position.
    • Disconnect: Suspect Light Bar Relay.
    • Carry out the light bar relay component test. Refer to COMPONENT TESTING .
    • Is the light bar relay OK? 

    Yes  : GO to AC8.

    No  : INSTALL a new light bar relay. TEST the system for normal operation.

  8. AC8 CHECK CIRCUIT 401 (PK) FOR AN OPEN 
    • Key in ON position.
    • Measure the voltage between the suspect light bar relay, harness side and ground as follows:
      RELAY TERMINALS AND CIRCUIT

      Suspect Relay Pin Circuit
      Light bar C1 86 401 (PK)
      Light bar C2 86 401 (PK)
      Light bar C3 86 401 (PK)
      Light bar C4 86 401 (PK)
      Light bar C5 86 401 (PK)
      Light bar C6 86 401 (PK)
      Light bar C7 86 401 (PK)
      Light bar C8 86 401 (PK)
      Fig 1: Checking Circuit 401 (PK) For An Open
      G04585540Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 

    Yes  : GO to AC9.

    No  : REPAIR the circuit in question. TEST the system for normal operation.

  9. AC9 CHECK THE LIGHT BAR RELAY BATTERY SUPPLY CIRCUIT FOR AN OPEN 
    • Measure the voltage between the suspect light bar relay connector, harness side and ground as follows:
      RELAY TERMINALS AND CIRCUIT

      Suspect Relay Pin Circuit
      Light bar C1 87 2300 (RD)
      Light bar C2 87 2300 (RD)
      Light bar C3 87 2300 (RD)
      Light bar C4 87 2300 (RD)
      Light bar C5 87 3258 (RD/YE)
      Light bar C6 87 3258 (RD/YE)
      Light bar C7 87 3258 (RD/YE)
      Light bar C8 87 3258 (RD/YE)
      Fig 2: Checking The Light Bar Relay Battery Supply Circuit For An Open
      G04585541Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 

    Yes  : GO to AC10.

    No  : REPAIR the circuit in question. TEST the system for normal operation.

  10. AC10 CHECK THE LIGHT BAR RELAY OUTPUT CIRCUITRY 
    • Connect a fused (10A) jumper wire between the inoperative light bar relay pin 87, harness side and the inoperative light bar relay pin 30, harness side.
      Fig 3: Checking The Light Bar Relay Output Circuitry
      G04585542Courtesy of FORD MOTOR CO.
    • Does the light bar lamp illuminate? 

    Yes  : REMOVE the jumper wire. GO to  AC13.

    No  : LEAVE the jumper wire connected. GO to AC11.

  11. AC11 CHECK THE FUSE INPUT CIRCUIT FOR AN OPEN 
    • Measure the voltage between the suspect light bar fuse, input side and ground as follows:
      FUSE AND CIRCUIT

      Suspect Fuse Circuit
      Light bar C1 3020 (LB)
      Light bar C2 3021 (GY/BK)
      Light bar C3 3022 (RD/YE)
      Light bar C4 3023 (BK/OG)
      Light bar C5 3024 (DB/LG)
      Light bar C6 3025 (YE/LG)
      Light bar C7 3026 (RD/PK)
      Light bar C8 3027 (RD/WH)
      Fig 4: Checking The Fuse Input Circuit For An Open
      G04585543Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 

    Yes  : GO to AC12.

    No  : REPAIR the circuit in question. TEST the system for normal operation.

  12. AC12 CHECK FOR VOLTAGE TO THE LIGHT BAR 
    • Disconnect: Light Bar.
    • Measure the voltage between the light bar and ground as follows:
      CIRCUITS

      Circuit
      3020 (LB)
      3021 (GY/BK)
      3022 (RD/YE)
      3023 (BK/OG)
      3024 (DB/LG)
      3025 (YE/LG)
      3026 (RD/PK)
      3027 (RD/WH)
    • Is the voltage greater than 10 volts? 

    Yes  : INSTALL a new light bar. TEST the system for normal operation.

    No  : REPAIR the circuit in question. TEST the system for normal operation.

  13. AC13 CHECK THE STROBE/LIGHT BAR CONTROL SWITCH 
    • Key in OFF position.
    • Connect: Suspect Light Bar Relay.
    • Disconnect: Strobe/Light Bar Control Switch C3257b.
    • Key in ON position.
    • Connect a fused (5A) jumper wire between the strobe/light bar control switch, harness side and ground as follows:
      RELAY AND STROBE LIGHT BAR CONTROLS SWITCH CONNECTORS AND CIRCUIT

      Suspect Relay Strobe/Light Bar Control Switch Connector-Pin Circuit
      Light bar C1 C3257b-1 3005 (VT/LG)
      Light bar C2 C3257b-2 3006 (VT/LG)
      Light bar C3 C3257b-3 3007 (VT/YE)
      Light bar C4 C3257b-4 3008 (VT)
      Light bar C5 C3257b-5 3009 (OG/RD)
      Light bar C6 C3257b-6 3011 (BK/OG)
      Light bar C7 C3257b-7 3012 (WH)
      Light bar C8 C3257b-8 3013 (GY/BK)
      Fig 5: Checking The Strobe/Light Bar Control Switch
      G04585544Courtesy of FORD MOTOR CO.
    • Does the light bar lamp illuminate? 

    Yes  : INSTALL a new strobe/light bar control switch. TEST the system for normal operation.

    No  : REPAIR the circuit in question. TEST the system for normal operation.

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