Troubleshooting Curt Trailer Wiring Harness that Has Light that Stays On All the Time
Updated 03/17/2026 | Published 03/07/2026
Question:
I’ve had this unit installed for about 5 years now. No issues. Today I used it as I would any other time during the day. I come home at night and see the rear drivers side red running light on on the tail light. I began troubleshooting. Once I unplugged the trailer wiring harness and used the factory plug the running light worked as it should. Thus isolating the issue to the trailer wiring harness and box. I later discovered my power wire near the box had disconnected from the long wire running to the battery. Fixed that. Still same issue with the tail light running light remaining on. Changed up the ground location. No fix. Could the trailer harness box have gone bad or shorted from the loose and disconnected power wire? Looking for some help. Otherwise I guess I’ll have to replace the whole harness and hope that helps.
asked by: Bob C
Expert Reply:
Hey Bob, I appreciate all the troubleshooting you did so far but basically the short answer is that you need a new # C56208 as yours has an internal short that isn't repairable. These are designed to "jump on the grenade" of a trailer wiring short and prevent it from making it to the vehicle wiring and causing more damage there. In a way these are like a one time fuse for trailer wiring. The loose power wire does seem to have something to do with it potentially as well.
Joe K.
3/12/2026
Had the same issue with my 2015 Jeep Cherokee where one side of the tail lights goes out. Looks like a product defect to me or planned that way.
Bob C.
3/17/2026
This was helpful. I ended up buying a new harness for the car and switched them out. No further issues.
Jameson C.
3/17/2026
Product Page this Question was Asked From
Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
- Custom Fit Vehicle Wiring
- Trailer Hitch Wiring
- Vehicle End Connector
- Powered Converter
- No Tow Package
- 4 Flat
- Plug and Lead
- Plug-In
- Visible
- CURT
more information >
Featured Help Information
Instructions
Continue Researching
- Search Results: trailer wiring
- Shop: Trailer Wiring
- Shop: Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
- Video: Trailer Wiring Harness Installation - 2015 Jeep Cherokee c56208
- Video: A Closer Look at the JR Products Gas Shock
- Search Results: rv door parts
- Search Results: rv door strut
- Search Results: compartment door gas struts
- Video: Feature Review Gas Shock
- Shop: Gas Shock - 40 lb Force - 12" Extended, 7.91" Compressed - Black Nitride
- Shop: Gas Shock - 20 lb Force - 15" Extended, 8.91" Compressed - Black Nitride
- Search Results: trailer hitch
- Article: Brake Controller 7- and 4-Way Installation Kit (ETBC7)
- Shop: Curt Powered Tail Light Converter with 4-Pole Flat Trailer Connector
- Q&A: What is the Difference Between a Class II and a Class III Hitch?
- Shop: Trailer Hitch
- Video: How to Choose a Trailer Brake Controller
- Q&A: What is the Difference Between a 4-Way and 7-Way Trailer Connector
- Shop: Universal Installation Kit for Trailer Brake Controller - 7-Way RV and 4-Way Flat - 10 Gauge Wires
- Article: Trailer Wiring Diagrams
- Search Results: trailer tires and wheels
- Article: How to Measure for Trailer Hitch Drop
- Shop: Suspension Enhancement
- Q&A: Lug Nut Torque Chart for Trailer Wheels
- Shop: Roadmaster 4-Diode Universal Wiring Kit for Towed Vehicles - 7-Way to 6-Way Coiled Adapter Cord
- Video: Curt T-Connector Vehicle Wiring Harness Review C56040
- Video: The Low-Down on the Curt Powered Tail Light Converter with 4-Pole Flat Trailer Connector
- Article: Wiring Trailer Lights with a 7-Way Plug (It's Easier Than You Think)
- Shop: Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
- Search Results: trailer jack
on Custom Fit Vehicle Wiring
Jeremy L.
3/12/2026
I have had this same issue with my Jeep Cherokee. Just to clarify, are you saying that the issue was found in the wiring of the trailer? I use the same trailer all of the time and have had to replace the wiring kit twice now for the same issue. Thanks!