Troubleshooting No Running Lights on Boat Trailer  

Question:

Expert Reply:

For both basic 4-pole and 7-way trailer wiring the tail/running lights are carried on their own separate circuit. Brake lights and turn signals share another circuit.

On 4-pole wiring the running light signals are carried on the brown wire that connects to the pin that is next to the white ground wire/pin. On 7-way wiring the running lights are carried on the pin at the 11-o-clock position as you look at the vehicle's socket (please refer to the linked photo).

The best way to go is to test the connector on your truck to see if the running light signals are present. You can use a circuit tester like # PTW2993. Have a helper turn on the truck lights to see if the running light signal is there at the trailer connector. If not check all fuses related to trailer/towing functions; also check the main ground for the wiring harness where it connects to the truck's frame. Make sure this is a tight connection to a clean bare metal surface that is free of paint, primer, undercoat, grease and rust. A bad ground can cause all sort of issues but it usually first affects running lights since they draw more power than brake and turn lights.

Sometimes there can be a corrosion issue INSIDE a trailer connector, where it can be very hard to see. Corrosion can cause a short that could take out one of the circuits. There are spray-on electrical contact cleaner products from companies like WD-40 and Caig and sometimes these can dissolve any built-up corrosion.

You can also clean the actual contacts on the wiring connectors to remove any oxidized build-up that can interfere with signal transmission.

Once you get it all working again you can protect all of those clean connections with dielectric grease like # 11755. This blocks water and dirt from causing another corrosion issue in the future.

expert reply by: Adam R

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