Pinpoint Test Y: The Individual Trailer Lamp Is Inoperative - LH Trailer Turn Signal/STOPLAMP/Hazard Flasher Lamp

WARNING: This page is about a different car, the 2006 Ford F550 Super Duty, 2006 Ford F450 Super Duty, and 2006 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

Y1 CHECK CIRCUIT 52 (YE) FOR VOLTAGE
- Disconnect: Trailer Tow C4098 (4-Pin).
- Disconnect: Trailer Tow C4099 (7-Pin).
- Key in OFF position.
- While applying the brake pedal, measure the voltage between the trailer tow C4098-2, circuit 52 (YE) (4-pin connector), harness side and ground; or between the trailer tow C4099-1, circuit 52 (YE) (7-pin connector), harness side and ground.
  
  Fig 1: Checking Circuit 52 (YE) For Voltage
  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 Y2.
Y2 CHECK THE TRAILER TOW LH TURN RELAY
- Disconnect: Trailer Tow LH Turn Relay C1188.
- Carry out the trailer tow LH turn relay component test.
- Is the trailer tow LH turn relay OK?
Yes : GO to Y3.

No : INSTALL a new trailer tow LH turn relay. TEST the system for normal operation.
Y3 CHECK CIRCUIT 9 (LG/OG) FOR AN OPEN
- While applying the brake pedal, measure the voltage between the trailer tow LH turn relay C1187-2, circuit 9 (LG/OG), harness side and ground.
  
  Fig 2: Checking Circuit 9 (LG/OG) For Open
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
Yes : GO to Y4.

No : REPAIR the circuit. TEST the system for normal operation.
Y4 CHECK CIRCUIT 1362 (DG/OG) FOR AN OPEN
- Measure the voltage between the trailer tow LH turn relay C1187-3, circuit 1362 (DG/OG), harness side and ground.
  
  Fig 3: Checking Circuit 1362 (DG/OG) For Open
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
Yes : GO to Y5.

No : VERIFY the BJB fuse 9 (20A) is OK. If OK, REPAIR the circuit. TEST the system for normal operation.
Y5 CHECK THE TRAILER LH TURN RELAY GROUND
- Measure the resistance between the trailer tow LH turn relay C1187-1, circuit 57 (BK), harness side and ground.
  
  Fig 4: Checking Trailer LH Turn Relay Ground
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
Yes : REPAIR circuit 52 (YE). TEST the system for normal operation.

No : REPAIR circuit 57 (BK). TEST the system for normal operation.