Troubleshooting Boat Trailer Lights That Blew Fuse  

Question:

Expert Reply:

If your trailer caused the vehicle's fuse for trailer lighting to blow, then there could be a fault on the trailer. Your best bet is to disconnect the trailer wiring from the tow vehicle and test the vehicle connector to confirm if it operates correctly on its own.

You'll need a circuit tester like # PTW2993 as well as a helper to activate the vehicle's lighting functions while you test the various pins on the connector. Please refer to the linked photo showing a 4-pole flat connector and the lighting function carried on each pin and also to the linked video showing how to use the tester. Running lights are carried on the brown wire; stop and turn signals both are carried on the green and yellow wires.

Ground your tester to the exposed pin and one by one test the three circuit while your helper turns the functions on and off. The brown wire should carry a steady signal when the headlights are on; the green wire should carry an on-and-off blinking signal when the right turn is activated or a steady signal when the brake is activated; the yellow wire should carry left turn and stop signals. If the wiring delivers the correct signals then you know to move on to the trailer's wiring. If the vehicle wiring is NOT working then please let me know the year/make/model/version of the car so I can help you get a new harness.

Start your trailer inspection at the connector itself, looking for any signs of even slight greenish or whitish discoloration on the contacts. Clean or replace as needed. Follow the wiring from the trailer connector all the way back to each light, looking for cracks or worn spots in the insulation. Especially check spots where the wires have to make sharp bends or where they may rub against the trailer frame. Repair or replace damaged wiring. Also check the individual lights on the trailer to ensure their wiring (or mounting hardware) is making a solid ground connection to the trailer frame. A ground should be made to bare metal for best conductivity.

You can also test the trailer lights without the vehicle by applying 12V power direct to the pins on the trailer's connector. You can use the car's battery or a spare 12V battery if you have one. If you choose to test the trailer in this way first you do not need a tester and this will eliminate the trailer as the source of the problem if its lights work correctly when tested with direct power input.

expert reply by: Adam R

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