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Right Turn Signal & Running Light No Working After Replacement


I recently completely rewired our old trailer with new lights, bulbs, etc and everything was working for the first week or so, but now the right turn signal light and running light dont work. Ive checked the connections from the truck and the trailer, looked along the wires and didnt see or feel any nicks, and even tested the wires with a multimeter and saw there was current running through them. I also tried buying a brand new passenger side light and bulbs and this didnt solve the problem either. I know the ground works as well, but when I was testing it I was just touching the wire to the trailer and didnt have it secured on the tongue. Im just not sure what the issue could be and dont want to completely redo a wiring job I did less than a month ago.


Expert Reply:

We can resolve this issue. This seems like a 12-volt continuity to the lights, or a grounding issue at the lights themselves.

Since you are having trouble with two different wires, but not all lights, I would double check your 12-volts to the right turn signal/brake light which is the green wire. I would also check the brown wire for the running lights. At the connector on the back of your vehicle check for 12 volts with your vehicle lights turned on. Then with the blinkers turned on. If you are getting 12 volts during these tests then this proves it if not your vehicle wiring, or the ground at the vehicle.

You will need to thoroughly clean the connectors on the vehicle side and trailer side. Any corrosion on the trailer connector or the vehicle connectors must be cleaned out to ensure a good connection. Be careful on the vehicle side not to short out the wires using a metal brush or liquids.

Next I would check the grounding at the individual lights. These must be attached to grounded metal on the trailer. Sometimes the screws that attach the light fixture to the trailer also act as the ground. Be sure those connections are clean.

Finally, while a faulty ground at the trailer frame usually means that no lights work, a dirty connection sometimes means that not all lights work. I would undo that connection and ensure there there is not dirt, grime, OR paint at that connection. A simple screw into the frame is not always enough.

If you are still having issues I would open the light lenses and measure for 12 volts there – with the lights on. If you have 12 volts at the connector and not the bulb socket, then you will need to check your other wires again.

I have attached a link to some diagrams for trailer wiring.

You mentioned that you have a multimeter, but some folks find a job specific tester easier and faster to use. Depending on the connector type you may like the Brophy # F4CT tester or Pollak 7-Way Circuit Tester # PK12741. I have attached a link to these product pages and to videos on how they work.

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