Diagnosing Malfunctioning Turn Signal and Brake Lights on Gooseneck Trailer  

Question:

Expert Reply:

Although the brake and turn signals work on the truck, I would recommend testing the 7-way connector on the truck to determine if the problem exists in the trailer wiring on the vehicle, or on the trailer. Use a circuit tester like part # PTW2993 and test the pins on your 7-way that are in the 3:00 and 9:00 position. With the right turn signal on you should see power on the pin on the 3:00 location. With the left turn signal activated, the pin in the 9:00 location should light up the tester. Each of the two pins should also show power when the brake pedal is pressed.

If you get no signal on the pins, you either have a blown fuse in the tow package or the connector is not wired correctly. Check the fuses that protect your tow package circuits and replace if needed. I have also linked you to our trailer wiring FAQ page that shows how a 7-way should be wired. If you do get a signal, the problem exists in the wiring on the trailer itself. You would need to trace each circuit from the connector on the trailer back to its lamp, looking for loose, broken or pinched wires. Look for wire with worn or cracked insulation and repair as necessary.

If you are using the # H20046 wire connector you referenced, keep in mind that it might not wire color for color to your trailer wiring. The connector would connect as follows: the white wire should be grounded to the trailer frame, the red wire should be connected to the left turn/brake light, the brown wire connects to the right turn/brake, the green wire carries the running light circuit, the blue wire carries the brake output voltage and the black wire carries the 12-volt power for any trailer accessories that need power. The yellow wire is an auxiliary that can be used for reverse lights or any other purpose.

expert reply by: Mike L

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