Pinpoint Test Ag: The Trailer Parking Lamps Are Inoperative

WARNING: This page is about a different car, the 2014 Lincoln MKX and 2014 Ford Edge. 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.

AG1 CHECK FOR VOLTAGE TO THE TRAILER TOW CONNECTOR
- Ignition OFF.
- Place the headlamp switch in the PARKING LAMPS ON position.
- Measure the voltage between the trailer tow C439-3 , circuit CAT17 (BN), harness side and ground.
  
  Fig 1: Measuring Voltage Between Trailer Tow C439-3, Circuit CAT17 (BN), Harness Side And Ground
  Courtesy of FORD MOTOR CO.
Is the voltage greater than 10 volts?
- Yes : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
- No : VERIFY the BJB fuse 84 (20A) is OK. If OK, GO to AG2 . If not OK, REFER to the SYSTEM WIRING DIAGRAMS to identify the possible causes of the circuit short.
AG2 CHECK THE TRAILER TOW PARKING LAMP RELAY
- Place the headlamp switch in the OFF position.
- Disconnect: Trailer Tow Parking Lamp Relay.
- Substitute a known good relay.
- Place the headlamp switch in the PARKING LAMPS ON position.
- Measure the voltage between the trailer tow C439-3 , circuit CAT17 (BN), harness side and ground.
  
  Fig 2: Measuring Voltage Between Trailer Tow C439-3, Circuit CAT17 (BN), Harness Side And Ground
  Courtesy of FORD MOTOR CO.
Is the voltage greater than 10 volts?
- Yes : REMOVE the known good relay. INSTALL a new trailer tow parking lamp relay. TEST the system for normal operation.
- No : REMOVE the known good relay. GO to AG3 .
AG3 CHECK FOR VOLTAGE TO THE PARKING LAMP RELAY COIL
- Measure the voltage between the trailer tow parking lamp relay pin 1, circuit CBP30 (YE/BU), BJB face side and ground.
  
  Fig 3: Measuring Voltage Between Trailer Tow Parking Lamp Relay Pin 1, Circuit CBP30 (YE/BU), BJB Face Side And Ground
  Courtesy of FORD MOTOR CO.
Is the voltage greater than 10 volts?
- Yes : GO to AG4 .
- No : REPAIR circuit CBP30 (YE/BU) for an open. TEST the system for normal operation.
AG4 CHECK FOR VOLTAGE TO THE PARKING LAMP RELAY
- Place the headlamp switch in the OFF position.
- Measure the voltage between the trailer tow parking lamp relay pin 3, circuit SBB84 (GN/RD), BJB face side and ground.
  
  Fig 4: Measuring Voltage Between Trailer Tow Parking Lamp Relay Pin 3, Circuit SBB84 (GN/RD), BJB Face Side And Ground
  Courtesy of FORD MOTOR CO.
Is the voltage greater than 10 volts?
- Yes : GO to AG5 .
- No : VERIFY the BJB fuse 84 (20A) is OK. If OK, INSTALL a new BJB . TEST the system for normal operation. If not OK, REFER to the SYSTEM WIRING DIAGRAMS to identify the possible causes of the circuit short.
AG5 CHECK THE TRAILER TOW PARKING LAMP RELAY GROUND CIRCUIT FOR AN OPEN
- Measure the voltage between the trailer tow parking lamp relay pin 3, circuit SBB84 (GN/RD), BJB face side and the trailer tow parking lamp relay pin 2, circuit GD120 (BK/GN), BJB face side.
  
  Fig 5: Measuring Voltage Between Trailer Tow Parking Lamp Relay Pin 3, Circuit SBB84 (GN/RD) And Pin 2, Circuit GD120 (BK/GN), BJB Face Side
  Courtesy of FORD MOTOR CO.
Is the voltage greater than 10 volts?
- Yes : REPAIR circuit CAT17 (BN) for an open. TEST the system for normal operation.
- No : REPAIR circuit GD120 (BK/GN) for an open. TEST the system for normal operation.