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Troubleshooting Trailer Wiring With Faulty Brake and Running Lights

Question:

I hooked up my trailer to my pickup I ha I have turning signal I have tail light but when I push on the break I lose my tail light if I turn the tail lights off I have brake lightsbut when I turn my tail light on I leave my brake light

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Expert Reply:

I recommend first checking the ground wire on your trailer. The brake lights and running lights signals on your trailer do not run on the same wire, so it is unusual that they interfere with each other. A faulty ground connection can be the cause of many different issues. Check that the ground connections from your vehicle and trailer side connectors, and from your trailer lights, are attached to clean, bare metal surfaces such as the vehicle or trailer frame. Make sure that there is no dirt or debris built up on the ground connections. You can clean or sand off those grounding points to ensure bare metal to metal contact.

If the ground connection is clean and in good condition, then you will want to test the vehicle end trailer connector. Testing the connector on the vehicle will help determine if the problem is on the truck or on the trailer. You can use a circuit tester, like # PTW2993, to make sure signals are correct at the connector. It is easiest if you can have a friend help with this, that way your helper can press the brake and operate turn signals while you use the circuit tester at the rear of the vehicle. Traditionally, the brown wire signals the running/tail light, the green wire is the right turn and brake, and the yellow wire is the left turn and brake light.

If your signals are fine on the vehicle's trailer connector, you will then want to check the wires on your trailer. Make sure that none of the wires are pinched, frayed, or cut. A damaged wire can cause a short in your system. With the trailer unplugged, you can use a car battery or spare battery to provide 12V power directly to the trailer connector's various circuits. This is one way you can test the wiring on the trailer. You could also hook the trailer up to a different vehicle that has a fully functioning wiring harness.

I have attached a help article on troubleshooting 4-way wiring for you. If you have any other issues or these steps do not solve your problem, let me know and we can look into further troubleshooting steps for you.

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