Troubleshooting Trailer Turn and Brake Lights That Work But No Running Lights
Updated 03/12/2025 | Published 01/05/2025
Question:
I purchased your Curt wiring harness 56523 for my 2024 VW Jetta. The trailer turn signals and brake lights work, but the running lights do not. Power supply and ground are both good. What do you recommend to get the running lights working? Please note Step 6 in the instruction manual states that the wiring end with the brown and red wires should be ed between the taillight connectors, but there is no connector with brown and red wires on the harness. The end with yellow wires is attached on the driver side and the end with green wires is attached on the passenger side, as instructed by steps 7 and 8.
asked by: Tom B
Expert Reply:
Tom, It very well could be a tow package fuse on the vehicle. Though I'd start by checking all the connections and unplug the harnesses to make sure there is no debris or bent pins on vehicle side or harness side and plug everything back in and check again.
If all that looks good then I'd suggest using the owner's manual to find the locations of the fuses/relays related to the tow package wiring, and check them. If they are blown, then replace them and try again.
If the issue is not a fuse or relay then you can test the vehicle side trailer connector using a circuit tester # PTW2993. Turn the vehicle headlights on and use the circuit tester to test the pins on the connector at the back. If there is no power on the running light pins then there is a break or loose connection somewhere between the connector and where it terminates at the front of the vehicle that you will need to track down.
Tom B.
1/7/2025
Bryce, I checked the tow package fuse and it is good. Otherwise, the brake and turn signals would not work. The tow wiring harness is being powered directly from the battery, so there are no relays to be concerned about. I have used a voltmeter to test each terminal on the trailer connector. The brake and turn signals have power, but the running lights terminal does not. The trailer connector wires come directly from the converter box, and there are no breaks in the wires. I see that you had a question from a previous customer concerning this same wiring harness, Roberto on 8/7/24 with a similar problem where brakes and turn signals worked, but running lights did not. Looking at the powered converter, I don't see where it gets an input from the vehicle running lights. The only input wires are green, yellow, and white, which correspond to right turn signal, left turn signal, and ground. According to the wiring diagram on page 5 of the instruction manual, it shows an additional wire for running lights. Since my converter does not have this wire, where is it getting an input for running lights?