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Ho Do You Get the Running Lights to Work on a Cargo Trailer


how do you get the running lights to work


Helpful Expert Reply:

Trailer taillights have 3 functions in them, one of them being the running lights. The other 2 being combined brake lights and turn signals. Usually on a trailer the brown wire is for the running lights though there isn't exactly a standard for wire color and function, and it could be any color wire.

On a 4-Way flat connector the pin right next to the ground pin is the running light circuit. On a 7-Way trailer side, if looking at the back where the wires attach, the running light circuit is in the 11 o'clock position. These are the 2 most common trailer connectors. The functions of others can be seen in the link I have provided.

Whatever connector is on the trailer the vehicle side corresponding connector will need to have the circuit active or the lights on the trailer will not work. If the problem is that the running lights are not working on the trailer there are some tests you can do to determine where the problem is.

Use a circuit tester such as # PTW2993 to test the vehicle side connector while the running lights on the vehicle are on. If there is no power at the vehicle side connector when testing then it could be a blown fuse, damaged wire, or loose connection.

If there is power on the vehicle side, then the issue is on the trailer, most likely a bad ground. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light but can show up any time.

Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces.

The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

If the vehicle does not have a trailer connector one will need to be installed. I would need to know the year, make, and model of the vehicle and the type of connector the trailer has to recommend one.

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