Troubleshooting Non-Functioning Trailer Left Turn Signal on 2005 Toyota Tundra with Tow Package

Updated 08/04/2015 | Published 08/03/2015

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Question:

I have a 2005 Toyota Tundra with a factory trailer wiring. It has the plug adapter that accepts the round adapter to a 4 way. My left turn signal on trailers has stopped working. I have tried 3 different plugs, still not working. Cleaned the 2 plugs under the truck where the hookup for the adapter connects. All looked good. Any advise where to check. Is it possible the factory plug adapter hasa gone bad ? Thanks

asked by: Allan

Expert Reply:

It is certainly possible that a 10-year-old factory trailer connector can go bad. Sometimes internal corrosion or damage may not be visible. We do offer replacements for the factory wiring in tow-package-equipped Tundras, such as Hopkins # HM43385 and Tow Ready # 20137, which plug in to the OEM connectors. Both of these include 7-way and 4-pole connectors.

First, I suggest you check for blown fuses and replace any as needed. If this does not fix the problem, you can test the truck's wiring at those OEM connectors to see if the signals are making it to that point. A tester like # PTW2993 can be applied at the OEM connector contacts. The square connector with 4 contacts carries the taillight and turn/stop signals (please see the linked photo showing the mating connector). If there is no signal here you may need to replace a fuse, or it is possible that there could be damage to the truck's wiring.

You can also test the trailer easily enough by disconnecting it from the truck and applying 12V power direct to the contacts on the trailer plug. If the left turn signal on the trailer works with this direct power input then you know the issue is likely upstream of the trailer in the vehicle wiring or its trailer connector.

expert reply by: Adam R