Left Turn & Stop Lights on Gooseneck Trailer Do Not Work After Installation of New Wiring Harness

Question:

2010 Dodge Ram Factory installed tow package. Recently purchased goose neck horse trailer. Had a trailer sales business install a second plug in the truck bed. Left turn and break light does not work on the left side of trailer. Plugged in two another vehicle and everything works on the trailer. Factory installed plug was working fine prior to adding the other plug.

asked by: Billie B

Expert Reply:

The type of gooseneck and 5th wheel wiring harness you referenced, part # PK11932 from Pollak, plugs in at your bumper-mounted factory 7-way and provides duplicate wiring functions for the second 7-pole connector in the bed of your truck.

This kind of harness takes the signals that are present (or not) at your factory 7-way and just routes them up to the bed. These harnesses typically use a plug-in connection that installs without the need to cut or splice wires. Round U.S. Car Connectors are the type employed in the Pollak harness.

I suggest you unplug the secondary harness and test your truck's factory 7-way wiring at the bumper. If the left turn and stop signals are present on the truck's 7-way then the added harness is suspect. It should be inspected and cleaned or replaced. If the turn and stop signals are not working on the truck's original wiring then you'll need to troubleshoot that connector and/or the wiring leading to it.

A circuit tester like # PTW2993 makes testing much easier. The linked video and article illustrate how to use the tester and outline methods for troubleshooting.

Have a helper activate the left turn signal while you apply the grounded circuit tester to the pin at the 9-o-clock position (please refer to the linked photo). If no signal is present on the connector pin then test the yellow wire leading to it at the back of the connector. You want to keep testing upstream until you find the point where the signal is being lost.

Even slight greenish or whitish discoloration on the connector's contact surfaces can indicate corrosion that is severe enough to interfere with signals. You can try cleaning these with a spray on contact cleaner and a small brush to remove the oxidation or corrosion. Be sure to check both sides of the connector. You can also check the power distribution box in the engine compartment for any blown or corroded fuses for the tow package and replace as needed.