Pinpoint Test Z: The Trailer Lamps Are Inoperative - RH Trailer Turn/Stoplamp

WARNING: This page is about a different car, the 2004 Mercury Mountaineer and 2004 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.

Z1 CHECK VOLTAGE TO TRAILER TOW CONNECTOR
- Disconnect: Trailer Tow C439 (4-Pin Connector).
- Disconnect: Trailer Tow C473 (7-Pin Connector).
- While applying the brake pedal, measure the voltage between the trailer tow C439-4, circuit 64 (DG), harness side and ground (4-pin connector); and between the trailer tow C473-4, circuit 64 (DG), harness side and ground (7-pin connector).
  
  Fig 1: Checking Voltage To Trailer Tow Connector
  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

GO to Z2.
Z2 CHECK CIRCUIT 64 (DG) FOR AN OPEN
- Disconnect: Trailer Tow RH Turn Relay C1187.
- Measure the resistance between the trailer RH turn relay C1187-5, circuit 64 (DG), harness side and the trailer tow C439-4, circuit 64 (DG) (4-pin connector), harness side, or the trailer tow C473-4, circuit 64 (DG) (7-pin connector), harness side.
  
  Fig 2: Checking Circuit 64 (DG) For An Open
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
Yes

GO to Z3.

No

REPAIR the circuit. TEST the system for normal operation.
Z3 CHECK THE TRAILER TOW RH TURN RELAY
- Carry out the trailer tow RH turn relay component test.
- Refer to COMPONENT TESTING for schematic and connector information.
- Is the relay OK?
Yes

GO to Z4.

No

INSTALL a new trailer tow RH turn relay. TEST the system for normal operation.
Z4 CHECK FOR VOLTAGE ON CIRCUIT 175 (BK/YE)
- Measure the voltage between the trailer tow RH turn relay C1187-3, circuit 175 (BK/YE), harness side and ground.
Fig 3: Checking For Voltage On Circuit 175 (BK/YE)
Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
Yes

GO to Z5.

No

REPAIR the circuit. TEST the system for normal operation.
Z5 CHECK FOR VOLTAGE ON CIRCUIT 378 (BN/YE)
- While applying the brake pedal, measure the voltage between the trailer tow RH turn relay C1187-1, circuit 378 (BN/YE), harness side and ground.
  
  Fig 4: Checking For Voltage On Circuit 378 (BN/YE)
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
Yes

REPAIR circuit 1205 (BK). TEST the system for normal operation.

No

REPAIR circuit 378 (BN/YE). TEST the system for normal operation.