How to Test a 7 Way Trailer Plug

Updated 05/10/2021 | Published 05/07/2021

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Curt Trailer Hitch Receiver - Custom Fit - Class III - 2"

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Hook Probe Circuit Tester

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Question:

I plugged my 7 way in upside down on my fifth wheel. Only a for a few miles, then realized something was wrong. Now drivers side LED tail light not working properly. Have I shorted something out. All other lights seem to work. Thanks

asked by: Steven T

Helpful Expert Reply:

If the 7 Way Trailer Plug was installed upside-down, it definitely could have shorted something out. Using something like the circuit tester # PTW2993, you will first need to check all the ports on your 7 Way vehicle side plug. The 2 o'clock position will be your 12-volt power, the 3 o'clock position will be the right turn signal and right brake signal, the 5 o'clock position will be your brake controller output, the 7 o'clock position will be your ground, the 9 o'clock position will be the left turn signal and left brake, the 11 o'clock position will be the taillight and running lights, and the center position will be the auxiliary circuit. If one or more of these are not working, you will need to then check the fuses that correspond to towing in your owner's manual.

If all that tested good and all the fuses are in good condition, you will need to check the wiring and lights on the fifth wheel. In your case, the best thing to do will be to pull off the driver side light and test the wires going into the light. If there is power in the wires, you will need to replace the light. If there is no power, you will need to trace the wires back to see if they shorted out and broke connection. Odds are the LED just needs to be replaced though.

expert reply by: Lazer S