Troubleshooting Trailer Running Light Function When Bulb Has Been Tested

Updated 04/13/2018 | Published 04/12/2018

Products Featured in This Question

Hook Probe Circuit Tester

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$13.94

16 Gauge Primary Wire - Black - Per Foot

(64)

$1.10

Question:

My boat trailer running light on one side does not work although the blinker and brake light works. I have switched lights to check for faulty bulb but works fine. Worked for hours but cant figure it out, help

asked by: Mike

Expert Reply:

It sounds like you may have a bad running light wire or a bad ground. If you have adequate power when you check the power on that running light wire using a circuit tester like # PTW2993, then a ground wire is likely at fault. Even a ground that appears good and allows some light functions can be bad and miss one function. Running lights don't pull the same amount of power as a stop light and turn signal, so it is likely the ground is the issue. Make sure your connection is bare metal to metal and free of all corrosion, rust, and debris.

If you confirm the ground is good, then I recommend following that running light wire and testing it every couple of feet for function by using the circuit tester to probe the insulation. You may have a wire short that is interrupting power. Replace as needed using # 16-1-1.

expert reply by: Jason S