Only Left Side Brake and Turn Signals Working on Boat Trailer

Question

Question:

I have a new boat trailer 5pole also trailer brakes.All worked fine for a few weeks. One night while backing up boat trailer noticed only brake lights were working. was in hurry so unhooked and left. Next day hooked trailer back up to truck and only had left side brake and turn signal. Needing to leave I hooked it to second truck turned on headlights all lights on trailer came on and imediatly went off again with same brake and turn signal only thing working. Then was stupid and hooked to third vehicle same results. Then hooked up all three vehicles to utiliy trailer and nothing worked right . I am sure there are blown fuses but what would cause this. Thanks

asked by: Alan G

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Expert Reply:

This sounds like a ground problem. A loose, broken, or corroded ground connection can cause all sorts of unwanted problems for electrical components including trailer taillights.

I would start with checking for a proper ground at the taillight itself. Trailer tail lights can be grounded in one of two ways. The first way is the tail light assemblies can be grounded by a separate wire coming out of the back of the tail light and attached to the trailers frame. The second way is the tail lamp assembly is grounded through the mounting bolt that attaches the tail light to the frame.

You will also want to check the ground at the front of the trailer for any dirt or corrosion. Finally, check to make sure the actual connectors on both the truck and trailer are clean and free of corrosion. A bad ground or dirty connections are the two most common causes of lights not functioning properly.

I am including a couple of links to videos on troubleshooting the ground wire that should help. Also, a link to a FAQ page on trailer wiring.

After correcting the trailer lighting problem you will want to check the fuses in the vehicles to see if they will need to be replaced.

expert reply by: Jeff D

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Answer 1

On a trailer the brake lights and turn signals operate on the same wire/bulb. So, it is odd when the turn signals work, but the brake lights don't. There are 3 possible causes for this that are more likely than any of the other possible…

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Answer 2

Try improving the connection of the main ground wire of the trailer wiring harness. Make sure it is attached to a clean metal surface. Or you can run all of the trailer wires back to the main ground. This is actually the ideal solution. But you can…

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Answer 3

Trailers use a combined wiring system meaning the brake lights and turn signals are on the same circuits. Since the brake lights are working on the trailer, and because you have tested the vehicle wiring and it is working properly, there is most…

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Answer 4

In regards to wiring a seven way trailer connector, the twelve volt power wire or otherwise known as the battery charge line circuit will need to be run from the trailer connector to the positive terminal of the battery. The ground wire circuit…

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Answer 5

I wish the fuse would have blown instead of what seems to be the converter box but in your situation that's just how it seems to have gone. You can test this with a circuit tester like #PTW2993 for voltage on the input side of the box as well…

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Answer 6

It sounds like there is a short that is drawing power to the driver side tail light. Since harness #118552 is a powered harness and is connected the the vehicle battery a short would draw power even with the vehicle off. The first thing you are going…

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Answer 7

In some instances the trailer will try to ground itself between the hitch ball and coupler if the trailer's own ground connection is weak or poor. The best solution is to re-establish the trailer's own ground connection. Find the…

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Answer 8

In some cases trailer lighting will ground through the hitch ball but that's typically only if the actual ground circuit is insufficient. This is not an ideal setup. It needs to ground through the wiring of the trailer harness. You can test this…

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Answer 9

Your brake lights and turn signals for each side are on one circuit. The left side turn signal and brake light is generally the yellow wire going into your trailer connector. The first thing to do is check the fuses on your tow vehicle. Next, inspect…

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Answer 10

Since LED lights do not require a lot of amperage you can go with relatively small wire. Using 16 or 18 gauge wire will be fine. Harness #A20WB uses 20 gauge wire which is on the small side but certainly not a problem at all for LED lights even…

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Answer 11

Thank you for all of the details in your question. It looks like you have a faulty ground or some corrosion in one of your connectors. On a trailer the functions for your turn signals are also tied into the brake lights so if your right turn signal…

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Answer 12

Most trailer wiring problems are the result of a bad ground. What I would do is start with the connectors. Maker sure the connectors on both the trailer side and vehicle side are free of dirt and corrosion and that they are properly grounded. Next, I…

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Only Left Side Brake and Turn Signals Working on Boat Trailer

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