Troubleshooting Malfunctioning Running Light Circuit on Trailer

Question:

I installed the T one connector No.118482 as instructed to my 2012 Toyoya Avalon. I hooked the trailer up and I had brake lights and turn signal ligts to the trailer but no running lights to the trailer. The running lights on the car are functioning. Any suggestions?

asked by: Robert C

Expert Reply:

For starters, check the T-connectors and make sure they are fully plugged in until they click.

Secondly, test the 4-pole using a circuit tester like part # PTW2993. Turn on the vehicle headlights and test the pin on the 4-pole that is fed by the brown wire. If you get voltage on that pin, you have ruled out the vehicle as being the problem.

At this point, you will need to trace the running light circuit on the trailer, which is typically a brown wire. Start at the trailer connector, looking for excessive corrosion or damage. Trace the wire back to the taillights, looking for pinched wires, or for cracked or worn insulation. Look for broken or loose connections.

If there is NO voltage on the running light socket on the connector, you will need to use your circuit tester to troubleshoot the converter box. Turn on your vehicle headlights, and use the tester to probe the brown wire on the INPUT side of the converter box. You should see voltage on this wire. Then, test the brown wire on the OUTPUT side of the converter box. If there is voltage entering, but not leaving the box, the box is faulty and should be replaced. If there is voltage entering and leaving the box, the plugs that attach the converter inline with the tail light assemblies are either loose or faulty. If this is the case, or if the converter box is faulty, please call our customer service folks for instructions on how to proceed.

If you should find that the box is faulty, make sure to examine the wiring on the trailer. The box might have shorted out due to a wiring problem on the trailer. If the converter is replaced before the wiring problem on the trailer is identified and repaired, you'll continue to blow up converters or possibly fuses in the tow vehicle.

I will link you to a video showing how to troubleshoot the converter box, as well as a troubleshooting FAQ article that should be helpful. Locating the cause of the problem you are experiencing might be a bit time consuming, but if you are methodical and rule one thing out at a time, you should be able to locate and correct the problem.

expert reply by: Mike L