Pinpoint Test Y: All The Trailer Lamps Are Inoperative

WARNING: This page is about a different car, the 2010 Mercury Mariner and 2010 Ford Escape. 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: Failure to disconnect the battery when instructed will result in false resistance readings. Refer to BATTERY, MOUNTING AND CABLES .

Y1 CHECK THE TRAILER TOW GROUND CIRCUITS FOR AN OPEN
- Disconnect: Trailer Tow C439.
- Disconnect: Negative Battery Cable.
- Measure the resistance between the trailer tow C439-4, circuit RAT08 (WH), harness side and ground.
  
  Fig 1: Measuring Resistance Between Trailer Tow C439-4, Circuit RAT08 (WH), Harness Side 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: REPAIR circuit RAT08 (WH) or circuit GD149 (BK/GY) for an open. TEST the system for normal operation.