Pinpoint Test Ab: The Trailer Lamps Are On Continuously

WARNING: This page is about a different car, the 2014 Ford F-150. 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.

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.

AB1 CHECK THE VEHICLE EQUIPMENT FOR A 7-PIN CONNECTOR
- Ignition OFF.
- Inspect the vehicle for a 7-pin trainer tow connector.
Is the vehicle equipped with a 7-pin trailer tow connector?
- Yes : GO to AB3.
- No : GO to AB2 .

AB2 CHECK FOR VOLTAGE AT THE TRAILER TOW 4-PIN CONNECTOR

Ignition ON.

Measure the voltage between the trailer tow 4-pin connector, harness side and ground as follows:

Connector-Pin	Circuit
C439B-1 (RH stop/turn lamp)	CAT09 (GN)
C439B-2 (LH stop/turn lamp)	CAT06 (YE)
C439B-3 (parking lamps)	CAT17 (BN)

Fig 1: Measuring Voltage Between Trailer Tow 4-Pin Connector, Harness Side And Ground

Courtesy of FORD MOTOR CO.

Is any voltage present?

Yes : GO to AB4.
No : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.

AB3 CHECK FOR VOLTAGE AT THE TRAILER TOW 7-PIN CONNECTOR
- Ignition ON.
- For the LH trailer stop/turn lamp, measure the voltage between the trailer tow connector LH stop/turn lamp voltage supply pins, circuit CAT06 (YE), component side and ground.
  
  Fig 2: Measuring Voltage Between Trailer Tow Connector LH Stop/Turn Lamp Voltage Supply Pins, Circuit CAT06 (YE) And Ground
  Courtesy of FORD MOTOR CO.
- For the RH trailer stop/turn lamp, measure the voltage between the trailer tow connector RH stop/turn lamp voltage supply pins, circuit CAT09 (GN), component side and ground.
  
  Fig 3: Measuring Voltage Between Trailer Tow Connector RH Stop/Turn Lamp Voltage Supply Pins, Circuit CAT09 (GN) And Ground
  Courtesy of FORD MOTOR CO.
- For the trailer parking lamps, measure the voltage between the trailer tow connector parking lamp voltage supply pins, circuit CAT17 (BN), component side and ground.
  
  Fig 4: Measuring Voltage Between Trailer Tow Connector Parking Lamp Voltage Supply Pins, Circuit CAT17 (BN) And Ground
  Courtesy of FORD MOTOR CO.
- For the trailer reversing lamps, measure the voltage between the trailer tow connector reversing lamp voltage supply pin, circuit CAT16 (GY/BN), component side and ground.
  
  Fig 5: Measuring Voltage Between Trailer Tow Connector Reversing Lamp Voltage Supply Pin, Circuit CAT16 (GY/BN) And Ground
  Courtesy of FORD MOTOR CO.
Is any voltage present?
- Yes : GO to AB4 .
- No : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
AB4 CHECK THE SUSPECT RELAY
- Ignition OFF.
- Disconnect: Suspect Trailer Tow Relay.
- Carry out the component test for the suspect trailer tow relay.
  Refer to OEM WIRING DIAGRAMS COMPONENT TESTING for component testing.
Is the trailer tow relay OK?
- Yes : REPAIR circuit CAT06 (YE) (LH stop/turn), circuit CAT09 (GN) (RH stop/turn), circuit CAT17 (BN) (parking lamps) or CAT16 (GY/BN) (reversing lamps) for a short to voltage. TEST the system for normal operation.
- No : INSTALL a new trailer tow relay in question. TEST the system for normal operation.