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Pinpoint Test U: The Trailer Lamps Are Inoperative - Trailer Reversing Lamps

WARNING: This page is about a different car, the 2008 Ford RV Cutaway, 2008 Ford Econoline, 2008 Ford E450 Super Duty, and 2008 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
  1. U1 CHECK THE TRAILER PARKING LAMPS 
    • Key in OFF position.
    • Place the headlamp switch in the PARKING LAMPS ON position.
    • Do the trailer parking lamps operate correctly? 
    1. YES  : Go to  U2.
    2. NO  : Go to Pinpoint Test T .
  2. U2 CHECK FOR VOLTAGE TO THE TRAILER 
    • Place the headlamp switch in the OFF position.
    • Disconnect the trailer from the vehicle.
    • Apply the parking brake.
    • Key in ON position.
    • Select REVERSE.
      • Fig 1: Measuring Voltage Between Trailer Tow C4099-7, Circuit 963 (BK/LG)
      GF0041147Courtesy of FORD MOTOR CO.
    • Measure the voltage between the trailer tow C4099-7, circuit 963 (BK/LG), component side and ground.
    • 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  : Go to  U3.
  3. U3 CHECK THE TRAILER TOW REVERSING LAMP RELAY 
    • Select PARK.
    • Key in OFF position.
    • Disconnect: Trailer Tow Reversing Lamp Relay
    • Substitute a known good relay and recheck the trailer tow reversing lamp operation.
    • Do the trailer tow reversing lamps operate correctly? 
    1. YES  : REMOVE the known good relay. INSTALL a new trailer tow reversing lamp relay. TEST the system for normal operation.
    2. NO  : REMOVE the known good relay. Go to  U4.
  4. U4 CHECK CIRCUIT 1043 (DG/YE) FOR AN OPEN 
      Fig 2: Checking Circuit 1043 (DG/YE) For An Open
      GF0012897Courtesy of FORD MOTOR CO.
    • Measure the voltage between the trailer tow reversing lamp relay pin 3, circuit 1043 (DG/YE), BJB face side and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  U5.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  5. U5 CHECK CIRCUIT 57 (BK) FOR AN OPEN 
      Fig 3: Checking Circuit 57 (BK) For An Open
      GF0012898Courtesy of FORD MOTOR CO.
    • Measure the resistance between the trailer tow reversing lamp relay pin 2, circuit 57 (BK), BJB face side and ground.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  U6.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  6. U6 CHECK FOR VOLTAGE TO THE TRAILER REVERSING LAMP RELAY 
    NOTE: Make sure the parking brake is still applied.
    • Key in ON position.
    • Select REVERSE.
      • Fig 4: Checking For Voltage To Trailer Reversing Lamp Relay
      GF0012899Courtesy of FORD MOTOR CO.
    • Measure the voltage between the trailer tow reversing lamp relay pin 1, circuit 140 (BK/PK), BJB face side and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : REPAIR circuit 963 (BK/LG) for an open. TEST the system for normal operation.
    2. NO  : REPAIR circuit 140 (BK/PK) for an open. TEST the system for normal operation.
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