Troubleshooting Trailer Lights and Trailer Connector Installed on 2004 Toyota Sienna  

Question:

Expert Reply:

Typically, a load resistor like # DI34ZR isn't used unless the tow vehicle has a bulb out sensor. Because LED trailer lamps draw but a fraction of power used by incandescent bulbs, the bulb out sensor thinks there's a bulb burned out in the system and makes the turn signals hyperflash.

I don't think this is the situation in your case. You'll need to do some basic troubleshooting, beginning with the trailer connector on your vehicle. Unplug the trailer and use a circuit tester like part # PTW2992 on the pins of the connector as a helper activates each lighting function (turn signals, running lamps, brakes). If all operates okay, then the problem lies somewhere in the wiring on the trailer. You'll need to carefully check the trailer wiring to ensure everything's wired correctly. It may sound blatantly obvious but check that each trailer lamp is wired correctly. On the # STL78RB lamp you mentioned, the red wire is the turn/brake lamp, and the black wire is the running lamp.

If the 4-pole doesn't function correctly, you'll need to trace the wiring from the 4 pole until you find the converter box. Activate the left turn signal and use your tester on the input side of the box on the yellow wire. Do the same for the right turn (green) and running lights (brown wire). If you get power entering, but not leaving the converter box, it means the converter has been shorted out and needs to be replaced. If the signals from each function are NOT entering the converter, check the connections where the converter plugs inline between the vehicle wiring and the taillight converter.

I'll link you to our trailer connector troubleshooting article, which you should find helpful. If none of the above helps you locate the problem, please get back with me.

expert reply by: Mike L

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