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Troubleshooting Left Turn Signal Problem When Using 7 to 4-Way Wiring Adapter PK12716 on a 2006 GMC

Question:

I have a 2006 GMC Sierra and, when I hook my cargo trailer everything works except the left turn signal.Can you tell what the problem might be? Thanks for all your help.

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Expert Reply:

To determine where the problem is occurring, I would use a circuit tester to check for function at a couple different points. You will either need to leave on the turn signal in the cab of your truck, or have a helper operate it for you. We offer circuit tester # 40376 if needed.

First, without the adapter or trailer connected, you can make sure that the left turn signal is reading correct at the 7-Way plug on your 2006 Sierra. The left turn signal is normally located at the second blade from the top, going counterclockwise.

If you get a good reading here, insert the adapter and test again. The left turn signal should be the second port from the top.

You will need to move your attention to the trailer side if the signal is reading correct at the adapter. Usually a bad ground connection on the trailer will be enough to cause a light to work erratically or not at all. Check the ground wire, usually white, on the trailer connector, as well as any ground wires or grounding hardware on the trailer lights to make sure they are free of corrosion, paint, and buildup, and that they are all still firmly attached to a clean metal area of the trailer frame.

Trailer lights are often grounded through the mounting hardware, so even something as simple as a plastic license plate bracket sandwiched between the light and the grounding surface could cause a ground problem.

You can view some additional information on wiring a trailer at the link below, as well as some diagrams that should be helpful for you.

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