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Pinpoint Test V: The Trailer Lamps Are Inoperative

WARNING: This page is about a different car, the 2007 Lincoln Mark LT and 2007 Ford Pickup. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
  1. V1 DETERMINE THE CONDITION 
    • Observe the trailer tow lamps and determine the inoperative lamp(s).
    • Are all of the trailer tow lamps inoperative? 
    1. YES  : Go to  V2.
    2. NO  : If the trailer LH stop/turn lamp is inoperative, go to  V3.

      If the trailer RH stop/turn lamp is inoperative, go to  V5.

      If the trailer parking lamps are inoperative, go to  V7.

      If the trailer reversing lamps are inoperative, go to  V14.

  2. V2 CHECK THE TRAILER TOW GROUND 
    • Disconnect: Trailer Tow C439b (4-Pin)
    • Disconnect: Trailer Tow C439a (7-Pin)
    • Measure the resistance between the trailer tow C439b-4 (4-pin), circuit 206 (WH), harness side and ground; or between the trailer tow C439a-2 (7-pin), circuit 206 (WH), harness side and ground.
      • Fig 1: Checking Trailer Tow Ground
      GF0004627Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    1. YES  : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  3. V3 CHECK THE VOLTAGE TO THE TRAILER TOW CONNECTOR (LH TURN) 
    • Disconnect: Trailer Tow C439b (4-Pin)
    • Disconnect: Trailer Tow C439a (7-Pin)
    • While applying the brake pedal, measure the voltage between the trailer tow C439b-2 (4-pin), circuit 52 (YE), harness side and ground; or between the trailer tow C439a-1 (7-pin), circuit 52 (YE), harness side and ground.
      • Fig 2: Checking Voltage To Trailer Tow Connector (LH Turn)
      GF0004628Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
    2. NO  : VERIFY the CJB fuse 42 (10A) is OK. If OK, go to  V4.
  4. V4 CHECK CIRCUIT 52 (YE) FOR AN OPEN 
    • Disconnect: CJB C270k
    • While applying the brake pedal, measure the voltage between the CJB C270k pin 2, circuit 52 (YE), component side and ground.
      • Fig 3: Checking Circuit 52 (YE) For An Open
      GF0004629Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : REPAIR the circuit. TEST the system for normal operation.
    2. NO  : REPAIR or INSTALL a new CJB. TEST the system for normal operation.
  5. V5 CHECK THE VOLTAGE TO THE TRAILER TOW CONNECTOR (RH TURN) 
    • Disconnect: Trailer Tow C439b (4-Pin)
    • Disconnect: Trailer Tow C439a (7-Pin)
    • While applying the brake pedal, measure the voltage between the trailer tow C439b-1 (4-pin), circuit 64 (DG), harness side and ground; or between the trailer tow C439a-4 (7-pin), circuit 64 (DG), harness side and ground.
      • Fig 4: Checking Voltage To Trailer Tow Connector (RH Turn)
      GF0004630Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
    2. NO  : VERIFY the CJB fuse 36 (10A) is OK. If OK, go to  V6.
  6. V6 CHECK CIRCUIT 64 (DG) FOR AN OPEN 
    • Disconnect: CJB C270j
    • While applying the brake pedal, measure the voltage between the CJB C270j pin 16, circuit 64 (DG), component side and ground.
      • Fig 5: Checking Circuit 64 (DG) For Open
      GF0004631Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : REPAIR the circuit. TEST the system for normal operation.
    2. NO  : REPAIR or INSTALL a new CJB. TEST the system for normal operation.
  7. V7 CHECK THE VOLTAGE TO THE TRAILER TOW CONNECTOR (PARKING LAMPS) 
    • Disconnect: Trailer Tow C439b (4-Pin)
    • Disconnect: Trailer Tow C439a (7-Pin)
    • Place the headlamp switch in the PARKING LAMPS ON position.
    • Measure the voltage between the trailer tow C439b-3 (4-pin), circuit 962 (BN/WH), harness side and ground; and between the trailer tow C439a-6 (7-pin), circuit 962 (BN/WH), harness side and ground.
      • Fig 6: Checking Voltage To Trailer Tow Connector (Parking Lamps)
      GF0004632Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
    2. NO  : TURN the headlamp switch off. VERIFY the CJB fuse 10 (20A) is OK. If OK, go to  V8 .
  8. V8 CHECK THE TRAILER PARKING LAMP RELAY 
    • Disconnect: Trailer Parking Lamp Relay
    • Carry out the trailer parking lamp relay component test. Refer to COMPONENT TESTING.
    • Is the relay OK? 
    1. YES  : Go to  V9.
    2. NO  : INSTALL a new trailer parking lamp relay. TEST the system for normal operation.
  9. V9 CHECK THE HEADLAMP SWITCH OUTPUT 
    • Place the headlamp switch in the PARKING LAMPS ON position.
    • Measure the voltage between the trailer parking lamp relay pin 2, circuit 14 (BN), harness side and ground.
      • Fig 7: Checking Headlamp Switch Output
      GF0004633Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : TURN the headlamp switch off. Go to  V11 .
    2. NO  : TURN the headlamp switch off. Go to  V10 .
  10. V10 CHECK CIRCUIT 14 (BN) FOR AN OPEN 
    • Disconnect: CJB C270e
    • Place the headlamp switch in the PARKING LAMPS ON position.
    • Measure the voltage between the CJB C270e-2, circuit 14 (BN), harness side and ground.
      • Fig 8: Checking Circuit 14 (BN) For An Open
      GF0004634Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : REPAIR or INSTALL a new CJB. TEST the system for normal operation.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  11. V11 CHECK FOR TRAILER PARKING LAMP RELAY GROUND 
    • Measure the resistance between the trailer parking lamp relay pin 1, circuit 57 (BK), harness side and ground.
      • Fig 9: Checking Trailer Parking Lamp Relay Ground
      GF0004635Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  V12.
    2. NO  : REPAIR or INSTALL a new CJB. TEST the system for normal operation.
  12. V12 CHECK FOR VOLTAGE TO THE TRAILER PARKING LAMP RELAY 
    • Measure the voltage between the trailer parking lamp relay pin 3, harness side and ground.
      • Fig 10: Checking Voltage To Trailer Parking Lamp Relay
      GF0004636Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  V13.
    2. NO  : REPAIR or INSTALL a new CJB. TEST the system for normal operation.
  13. V13 CHECK CIRCUIT 962 (BN/WH) FOR AN OPEN 
    • Disconnect: CJB C270k
    • Connect a fused (20A) jumper wire between the trailer parking lamp relay pin 3, harness side and the trailer parking lamp relay pin 5, circuit 962 (BN/WH), harness side.
      • Fig 11: Checking Circuit 962 (BN/WH) For An Open (1 Of 2)
      GF0004637Courtesy of FORD MOTOR CO.
    • Measure the voltage between the CJB C270k pin 1, circuit 962 (BN/WH), component side and ground.
      • Fig 12: Checking Circuit 962 (BN/WH) For An Open (2 Of 2)
      GF0004638Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : REPAIR the circuit. TEST the system for normal operation.
    2. NO  : REPAIR or INSTALL a new CJB. TEST the system for normal operation.
  14. V14 CHECK FOR VOLTAGE TO THE TRAILER TOW CONNECTOR 
    • Disconnect: Trailer Tow C439a
    • Apply the parking brake.
    • Key in ON position.
    • Place the transmission in REVERSE (R).
    • Measure the voltage between the trailer tow C439a-7, circuit 140 (BK/PK), harness side and ground.
      • Fig 13: Checking For Voltage To Trailer Tow Connector
      GF0004639Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
    2. NO  : VERIFY the CJB fuse 10 (20A) is OK. If OK, go to  V15.
  15. V15 CHECK CIRCUIT 140 (BK/PK) FOR AN OPEN 
    • Key in OFF position.
    • Place the transmission in PARK (P).
    • Measure the resistance between the trailer tow C439a-7, circuit 140 (BK/PK), harness side and the CJB C270e-20, circuit 140 (BK/PK), harness side.
      • Fig 14: Checking Circuit 140 (BK/PK) For An Open
      GF0004640Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  V16.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  16. V16 CHECK CIRCUIT 1043 (DG/YE) FOR AN OPEN 
    • Key in ON position.
    • Place the transmission in REVERSE (R).
    • Measure the voltage between the CJB C270b-12, circuit 1043 (DG/YE), harness side and ground.
      • Fig 15: Checking Circuit 1043 (DG/YE) For An Open
      GF0004641Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    1. YES  : REPAIR or INSTALL a new CJB. TEST the system for normal operation.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
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