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PINPOINT TEST AM : The Trailer Battery Charging Is Inoperative Or Operates With The Ignition Off

NOTE: Before beginning diagnostics, visually inspect the trailer tow connector mounted on the bumper for signs of corrosion or damage. Repair or install a new trailer tow connector as required.

  1. AM1 CHECK FOR VOLTAGE THROUGH THE TRAILER TOW CONNECTOR (BATTERY CHARGE INOPERATIVE)

    • Start the engine.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      Trailer Tow Connector Pin 5
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is the voltage greater than 11 volts? 

    Yes  GO to  AM2.
    No  VERIFY the BJB fuse 24 (30A) is OK. If OK, GO to  AM5. If not OK, REFER to the OEM ELECTRICAL WIRING DIAGRAM INTRODUCTION to identify the possible causes of the circuit short.

  2. AM2 CHECK FOR VOLTAGE AT THE TRAILER TOW CONNECTOR (BATTERY CHARGE ALWAYS ON)

    • Ignition OFF.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      Trailer Tow Connector Pin 5
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is any voltage present? 

    Yes  GO to  AM3.
    No  The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.

  3. AM3 CHECK THE TRAILER TOW BATTERY CHARGE RELAY OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE

    • Disconnect: Trailer Battery Charge Relay.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      Trailer Tow Connector Pin 5
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is any voltage present? 

    Yes  REPAIR the circuit.
    No  GO to  AM4.

  4. AM4 CHECK FOR VOLTAGE TO THE TRAILER BATTERY CHARGE RELAY COIL (ALWAYS ON)

    • Measure:
      Positive Lead Measurement / Action Negative Lead
      Trailer Tow Battery Charge Relay Pin 2
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is any voltage present? 

    Yes  REFER to the OEM ELECTRICAL WIRING DIAGRAM INTRODUCTION to identify the possible causes of the circuit short.
    No  INSTALL a new trailer tow battery charge relay.

  5. AM5 CHECK FOR VOLTAGE AT THE TRAILER TOW CONNECTOR (BATTERY CHARGE INOPERATIVE)

    • Ignition OFF.
    • Disconnect: Trailer Tow Connector.
    • Start the engine.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C4099-5
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is the voltage greater than 11 volts? 

    Yes  INSTALL a new trailer tow connector. TEST the system for normal operation.
    No  GO to  AM6.

  6. AM6 CHECK THE TRAILER TOW BATTERY CHARGE RELAY

    • Ignition OFF.
    • Disconnect: Trailer Tow Battery Charge Relay.
    • Substitute a known good relay.
    • Start the engine.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      C4099-5
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is the voltage greater than 11 volts? 

    Yes  REMOVE the known good relay. INSTALL a new trailer tow battery charge relay.
    No  REMOVE the known good relay. GO to  AM7.

  7. AM7 CHECK THE TRAILER TOW BATTERY CHARGE RELAY VOLTAGE SUPPLY CIRCUIT FOR AN OPEN

    • Ignition OFF.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      Trailer Tow Battery Charge Relay Pin 3
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is the voltage greater than 11 volts? 

    Yes  GO to  AM8.
    No  REPAIR the circuit.

  8. AM8 CHECK THE TRAILER TOW BATTERY CHARGE RELAY COIL VOLTAGE SUPPLY CIRCUIT FOR AN OPEN

    • Ignition ON.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      Trailer Tow Battery Charge Relay Pin 2
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Ground

    Is the voltage greater than 11 volts? 

    Yes  GO to  AM9.
    No  VERIFY the BJB fuse 93 (5A) is OK. If OK, REPAIR the circuit. If not OK, REFER to the OEM ELECTRICAL WIRING DIAGRAM INTRODUCTION to identify the possible causes of the circuit short.

  9. AM9 CHECK THE BATTERY CHARGE RELAY COIL GROUND CIRCUIT FOR AN OPEN

    • Ignition OFF.
    • Measure:
      Positive Lead Measurement / Action Negative Lead
      Trailer Tow Battery Charge Relay Pin 3
      GFD37131Courtesy of FORD MOTOR COMPANY
      GFD33595Courtesy of FORD MOTOR COMPANY
      		 Trailer Tow Battery Charge Relay Pin 1
      GFD37131Courtesy of FORD MOTOR COMPANY

    Is the voltage greater than 11 volts? 

    Yes  REPAIR the trailer tow battery charge relay output circuit to the trailer tow connector for an open.
    No  REPAIR the trailer tow battery charge relay ground circuit for an open.
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