PINPOINT TEST AJ : The Trailer Reversing Lamps Are Inoperative Or Always On

WARNING: This page is about a different car, the 2017 Lincoln Navigator and 2017 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

AJ1 CHECK FOR VOLTAGE THROUGH THE TRAILER TOW CONNECTOR

Ignition OFF.

Disconnect: Trailer.

Apply the parking brake.

Ignition ON.

Place the gear selector lever in REVERSE.

Measure:

Positive Lead	Measurement / Action	Negative Lead
Courtesy of FORD MOTOR COMPANY Pin 7	Courtesy of FORD MOTOR COMPANY	Ground

Place the gear selector lever in PARK.

Measure:

Positive Lead	Measurement / Action	Negative Lead
Courtesy of FORD MOTOR COMPANY Pin 7	Courtesy of FORD MOTOR COMPANY	Ground

Is the voltage greater than 11 volts when the gear selector lever is in REVERSE and 0 volts when the gear selector lever is in PARK?

Yes	The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.
No	If the trailer reversing lamps are inoperative, GO to AJ2If the trailer reversing lamps are always on, GO to AJ6

AJ2 CHECK FOR VOLTAGE TO THE TRAILER TOW CONNECTOR (VEHICLE HARNESS)

Ignition OFF.

Disconnect: Trailer Tow Connector C4099 .

Apply the parking brake.

Ignition ON.

Place the gear selector lever in REVERSE.

Measure:

Positive Lead	Measurement / Action	Negative Lead
C4099-7	Courtesy of FORD MOTOR COMPANY	Ground

Is the voltage greater than 11 volts?

Yes	INSTALL a new trailer tow connector.
No	GO to AJ3

AJ3 CHECK THE TRAILER TOW REVERSING LAMPS RELAY

Place the gear selector lever in PARK.

Ignition OFF.

Disconnect: Trailer Tow Reversing Lamps Relay.

Substitute with a known good relay.

Apply the parking brake.

Ignition ON.

Place the gear selector lever in REVERSE.

Measure:

Positive Lead	Measurement / Action	Negative Lead
C4099-7	Courtesy of FORD MOTOR COMPANY	Ground

Is the voltage greater than 11 volts?

Yes	REMOVE the known good relay. INSTALL a new trailer tow reversing lamps relay.
No	REMOVE the known good relay. GO to AJ4

AJ4 CHECK THE TRAILER TOW REVERSING LAMPS RELAY VOLTAGE SUPPLY CIRCUITS

Place the gear selector lever in PARK.

Ignition OFF.

Disconnect: Trailer Tow Reversing Lamps Relay.

Apply the parking brake.

Ignition ON.

Place the gear selector lever in REVERSE.

Measure:

Positive Lead	Measurement / Action	Negative Lead
Courtesy of FORD MOTOR COMPANY Trailer Tow Reversing Lamps Relay, cavity 1	Courtesy of FORD MOTOR COMPANY	Ground
Courtesy of FORD MOTOR COMPANY Trailer Tow Reversing Lamps Relay, cavity 3	Courtesy of FORD MOTOR COMPANY	Ground

Are the voltages greater than 11 volts?

Yes	GO to AJ5
No	VERIFY the BJB fuse 31 (15A) is OK. If OK, REPAIR the circuit in question. If not OK, REFER to the OEM Electrical Wiring Diagram Introduction to identify the possible cause of the circuit short.

AJ5 CHECK THE TRAILER TOW REVERSING LAMPS RELAY GROUND CIRCUIT

Measure:

Positive Lead	Measurement / Action	Negative Lead
Courtesy of FORD MOTOR COMPANY Trailer Tow Reversing Lamps Relay, cavity 1	Courtesy of FORD MOTOR COMPANY	Courtesy of FORD MOTOR COMPANY Trailer Tow Reversing Lamps Relay, cavity 2

Are the voltages greater than 11 volts?

Yes	REPAIR the reversing lamps relay circuit between the reversing lamps relay and trailer tow connector.
No	REPAIR the circuit.

AJ6 CHECK THE TRAILER TOW REVERSING LAMPS RELAY OUTPUT CIRCUIT FOR A SHORT TO VOLTAGE

Place the gear selector lever in PARK.

Ignition OFF.

Disconnect: Trailer Tow Reversing Lamps Relay.

Ignition ON.

Measure:

Positive Lead	Measurement / Action	Negative Lead
Courtesy of FORD MOTOR COMPANY Pin 7	Courtesy of FORD MOTOR COMPANY	Ground

Is any voltage present?

Yes	REPAIR the circuit.
No	INSTALL a new trailer tow reversing lamps relay.