Trailer Running Lamp Circuit of 2018 Chevy 2500 Not Working At Trailer Connector

Updated 06/18/2025 | Published 08/21/2021

Products Featured in This Question

Pollak Replacement 7-Pole, RV-Style Trailer Connector Socket - Vehicle End

(739)

$16.12

Curt T-Connector Vehicle Wiring Harness for Factory Tow Package - 4-Pole Flat Trailer Connector

(717)

$37.90

Question:

My 2500 has the dual-terminal socket in the number 7-blade on top and 4-prong on bottom. I need both because I pull both a larger trailer and a small utility trailer. The tail lamp for both sockets no longer work and I get a warning on the dash that says ‘Check Trailer Wiring’. The dealer told me it was the trailer wiring but I tested both my trailers on other vehicles and had no issue. I also used a test light and there is no power to the tail lamp blade/prong for either. The turn signals, brake lights, reverse lights, all work. I’ve read of others having similar problems with this dual terminal setup. Do you have any recommendations? Thanks

asked by: Frank B

Expert Reply:

Lets begin with the non-functional trailer running lamp circuit. I'd suspect a fuse in the engine compartment fuse block in location # 15. Replace the fuse but before plugging the trailer back in, you'll want to closely examine the running lamp circuit on the trailer and its trailer connector to locate the short and repair it or you continually blow fuses. This could be an intermittent problem caused by a loose connection or some cracked or worn wire insulation on the wire in the running lamp circuit.

Because of the way the doors of the OEM socket are hinged, it isn't possible to open both the covers at the same time. The best way around this would be to install a T-harness like # C55384 which will plug in at the connection between the tow package harness and the trailer connector. This will allow you to use the 7-way as well as having access to a functional 4-pole at the same time.

I've linked to some trailer wiring and troubleshooting articles that you might find hepful.

expert reply by: Mike L