Troubleshooting Trailer Wiring

Updated 08/17/2026 | Published 08/02/2026

Question:

Hello, When I installed the C99DR Curt T-Connector Vehicle Wiring Harness with 4-Way Flat Trailer Connector today the passenger side turn signal no longer worked. With a trailer connected the passenger side turn signal operated on the trailer but the cars passenger turn signal still did not work. I verified that the passenger turn signal lights were not the issue by removing the t connector and connecting straight to the cars harness. I verified continuity between the pins on the passenger side t connectors but also noticed that the green wires were also showing as continuous. Is that correct or is there a short in the system somewhere? Any help with further troubleshooting would be greatly appreciated! Thanks!

asked by: Caleb U

Expert Reply:

Thank you for the detailed troubleshooting that was very helpful. Based on your testing that indicates the vehicle wiring and bulb are functioning properly, and the issue is occurring through the wiring harness

Regarding your continuity test, it is not unusual to measure continuity between some wires on a powered converter module because the internal solid-state electronics can provide a continuity path that is not a direct short. A continuity reading by itself is not enough to determine whether the converter has failed.

At this point, I would recommend:

Inspecting both passenger-side connectors to ensure no terminals have backed out, bent, or been damaged during installation.
Verifying the connectors are fully seated and latched.
If everything appears normal and the symptom remains exactly as you've described, the converter module or passenger-side leg of the harness may be defective.

expert reply by: Jameson C

Caleb U.

8/16/2026

I verified that the pins are straight and none are missing. I don't see any visible sign that the connector terminals are damaged. I reconnected the t writing to the car system and it seems to be working now, but it also worked last time for a day before no longer working. Do you know of something that could cause that? Would it be a loose connection or is there any other cause?

Jameson C.

8/17/2026

@CalebU intermittent working is odd but it usually means something isn't properly seated. I'd imagine you would have fixed it if that's the case by removing it and reinstalling it but let us know how that goes.