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

WARNING: This page is about a different car, the 2005 Mercury Mountaineer and 2005 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.

AC1 CHECK VOLTAGE TO TRAILER TOW CONNECTOR
- Disconnect: Trailer Tow C473.
- Apply the parking brake.
- Key in ON position.
- Select REVERSE.
- Measure the voltage between the trailer tow C473-7, circuit 963 (BK/LG), harness side and ground.
  
  Fig 1: Measuring Voltage Between Trailer Tow C473-7 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 : PLACE the transmission in PARK. GO to AC2.
AC2 CHECK THE REVERSING LAMPS RELAY
- Disconnect: Trailer Tow Reversing Lamp Relay C4023.
- Carry out the trailer tow reversing lamp relay component test. Refer to COMPONENT TESTING article.
- Is the relay OK?
- Yes : GO to AC3.
- No : INSTALL a new trailer tow reversing lamp relay. TEST the system for normal operation.
AC3 CHECK CIRCUIT 963 (BK/LG) FOR AN OPEN AND SHORT TO GROUND
- Key in OFF position.
- Measure the resistance between the trailer tow reversing lamp relay C4023-5, circuit 963 (BK/LG), harness side and the trailer tow C473-7, circuit 963 (BK/LG), harness side; and between the trailer tow reversing lamp relay C4023-5, circuit 963 (BK/LG), harness side and ground.
  
  Fig 2: Measuring Resistance Between Trailer Tow Reversing Lamp Relay C4023-5 And Trailer Tow C473-7
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms between the trailer tow reversing lamp relay and the trailer tow connector and greater than 10,000 ohms between the reversing lamps relay and ground?
- Yes : GO to AC4.
- No : REPAIR the circuit. TEST the system for normal operation.
AC4 CHECK CIRCUIT 1205 (BK) FOR CONTINUITY
- Measure the resistance between the trailer tow reversing lamp relay C4023-2, circuit 1205 (BK), harness side and ground.
  
  Fig 3: Measuring Resistance Between Relay Connector And Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : GO to AC5.
- No : REPAIR the circuit. TEST the system for normal operation.
AC5 CHECK CIRCUIT 1043 (DG/YE) FOR AN OPEN
- Measure the voltage between the trailer tow reversing lamp relay C4023-3, circuit 1043 (DG/YE), harness side and ground.
  
  Fig 4: Checking Relay Power Supply
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
- Yes : REPAIR circuit 140 (BK/PK). TEST the system for normal operation.
- No : REPAIR circuit 1043 (DG/YE). TEST the system for normal operation.