Pinpoint Test Ah: The Trailer Lamps Are On Continuously

WARNING: This page is about a different car, the 2014 Lincoln MKX and 2014 Ford Edge. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

AH1 CHECK FOR VOLTAGE AT THE TRAILER TOW CONNECTOR

Ignition ON.

Measure the voltage the between trailer tow connector, harness side and ground as follows:

Connector-Pin	Circuit
C439-2	CAT06 (YE)
C439-1	CAT09 (GN)
C439-3	CAT17 (BN)

Fig 1: Measuring Voltage Between Trailer Tow Connector, Harness Side And Ground

Courtesy of FORD MOTOR CO.

Is any voltage present?

Yes : GO to AH2 .
No : The vehicle is operating correctly. SEND the trailer to an authorized camper/trailer repair facility.

AH2 CHECK THE SUSPECT RELAY

Ignition OFF.
Disconnect: Suspect Trailer Tow Relay.
Ignition ON.

Measure the voltage the between trailer tow connector, harness side and ground as follows:

Connector-Pin	Circuit
C439-2	CAT06 (YE)
C439-1	CAT09 (GN)
C439-3	CAT17 (BN)

Fig 2: Measuring Voltage Between Trailer Tow Connector, Harness Side And Ground

Courtesy of FORD MOTOR CO.

Is any voltage present?

Yes : REPAIR circuit CAT06 (YE) (LH turn), circuit CAT09 (GN) (RH turn) or circuit CAT17 (BN) (parking lamps) for a short to voltage. TEST the system for normal operation.
No : INSTALL a new trailer tow relay in question. TEST the system for normal operation.