Pinpoint Test Ab: The Trailer Lamps Are Inoperative - Parking 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.

AB1 CHECK VOLTAGE TO TRAILER TOW CONNECTOR
- Disconnect: Trailer Tow C439 (4-Pin Connector).
- Disconnect: Trailer Tow C473 (7-Pin Connector).
- Turn the headlamp switch to the parking lamps ON position. Measure the voltage between the trailer tow C439-2, circuit 962 (BN/WH), harness side and ground (4-pin connector); and between the trailer tow C473-6, circuit 962 (BN/WH), harness side and ground (7-pin connector).
  
  Fig 1: Measuring Voltage Between Trailer Tow C439-2 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 headlamp switch in the OFF position. GO to AB2.
AB2 CHECK THE TRAILER PARKING LAMPS RELAY
- Disconnect: Trailer Tow Parking Lamp Relay C4022.
- Carry out the trailer tow parking lamp relay component test. Refer to COMPONENT TESTING article.
- Is the relay OK?
- Yes : GO to AB3.
- No : INSTALL a new trailer tow parking lamp relay. TEST the system for normal operation.
AB3 CHECK CIRCUIT 962 (BN/WH) FOR AN OPEN
- Measure the resistance between the trailer tow parking lamps relay C4022-87, circuit 962 (BN/WH), harness side and the trailer tow C439-2, circuit 962 (BN/WH) (4-pin connector), harness side, or the trailer tow C473-6, circuit 962 (BN/WH) (7-pin connector), harness side.
  
  Fig 2: Measuring Resistance Between Trailer Tow Parking Lamps Relay C4022-87 And Trailer Tow C439-2
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes : GO to AB4.
- No : REPAIR the circuit. TEST the system for normal operation.
AB4 CHECK CIRCUIT 1205 (BK) FOR CONTINUITY
- Measure the resistance between the trailer tow parking lamp relay C4022-85, 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 AB5.
- No : REPAIR the circuit. TEST the system for normal operation.
AB5 CHECK CIRCUIT 14 (BN) FOR VOLTAGE
- Turn the headlamp switch to the parking lamps ON position.
- Measure the voltage between the trailer tow parking lamp relay C4022-86, circuit 14 (BN), harness side and ground.
  
  Fig 4: Measuring Voltage Between Relay Socket Pin And Ground
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
- Yes : REPAIR circuit 1043 (DG/YE). TEST the system for normal operation.
- No : REPAIR circuit 14 (BN). TEST the system for normal operation.