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Troubleshooting a Truck 7-way for a Non Functioning Left Turn/Stop Circuit  


left signal light and brake light do not work rest of lights do want to see a diagram of the truck end of a 7 way hookup for trailer


Expert Reply:

I attached a picture of the front and back of a vehicle side 7-way for you to check out.

If you are looking at the front of your 7-way the left turn/brake signal is the one in the 9:00 position. I would recommend you test this circuit with a circuit tester like our part # PTW2992 while the left blinker of your vehicle is on and look for intermittent voltage. If there is not voltage then you know the problem is in your vehicle and the circuit should be traced back looking for damage and repaired as necessary.

If there is voltage there then you know the problem is on the trailer side of the equation. You will want to trace the circuit back and repair as necessary. The most common culprits are the trailer connector and the grounds of the light assemblies.

You may also find corrosion on either of the connectors. Sometimes this can create a short and can be fixed by cleaning it off.

I attached an FAQ article on wiring that you might find informative also.

expert reply by:
Jameson C
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