Troubleshooting 4-Pole Wiring That Lights Up LED Tester But Does Not Operate Trailer Lights  

Question:

Expert Reply:

A lighting tester that uses LEDs, like the one in your photo, will take very little power to illuminate. Test light LEDs are so sensitive that they will sometimes light up even when no signal is activated; this can occur from the low-level residual power that some wiring kits put out.

The powered 4-pole trailer wiring harnesses available for your 2014 Hyundai Tucson include Curt product # C56348 and Tekonsha # 118501.

If none of the trailer lights work, you can test to find the issue. Disconnect the trailer and vehicle plugs and test the trailer lights directly with 12V power from the car's battery or from a well-charged spare battery if you have one. Use wire to connect the battery NEG terminal to the ground pin on the trailer's 4-pole plug. Then, one by one, apply the POS terminal wire to the individual pins for the trailer's various light functions to see if they function.

If none of the trailer lights work when fed direct battery power, then you know the issue is likely to be on the trailer side. Check the main ground wire on the trailer to ensure it is solidly affixed to a clean bare metal surface. Weak grounds can cause all sort of lighting issues.

If the lights DO work with direct power, then you know to focus on the vehicle wiring. You can use a circuit tester like # PTW2992 (shown in the linked video) to test for correct output signals on the car's 4-pole. Test the left/input side of the controller to see if the vehicle signals are reaching the converter box. If so, then test the right/output side wires. If you have signals going in but not coming out, then the harness is damaged or its 12V power wire that runs up to the battery may be loose.

expert reply by: Adam R

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