Pinpoint Test X: All The Trailer Lamps Are Inoperative

WARNING: This page is about a different car, the 2013 Ford F-550 Super Duty, 2013 Ford F-450 Super Duty, 2013 Ford F-350 Super Duty, and 2013 Ford F-250 Super Duty. 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.

NOTE: Failure to disconnect the battery when instructed results in false resistance readings. Refer to BATTERY, MOUNTING AND CABLES .

X1 CHECK THE TRAILER TOW GROUND CIRCUIT FOR CONTINUITY TO GROUND
- Disconnect: Negative Battery Cable.
- Measure the resistance between the trailer tow connector ground supply pins, circuit RAT08 (WH), component side and ground.
  
  Fig 1: Measuring Resistance Between Trailer Tow Connector Ground Supply Pins And Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
- No : GO to X2.
X2 CHECK THE TRAILER TOW GROUND CIRCUIT FOR AN OPEN
- Disconnect: Trailer Tow C4099.
- Measure the resistance between the trailer tow C4099-2, circuit RAT08 (WH), harness side and ground.
  
  Fig 2: Measuring Resistance Between Trailer Tow C4099-2, Circuit RAT08 (WH) And Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : INSTALL a new trailer tow connector. TEST the system for normal operation.
- No : REPAIR circuit RAT08 (WH) for an open. TEST the system for normal operation.