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Strange Trailer Lighting Phenomena

jbonnot03

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Need some help/expertise...

2025 Ram 3500 Lone Star
I have an issue when hooked to 1 particular trailer. Every other trailer I have tried, lights work as should.

Background...Horses damaged lighting wires so I decided to rewire entire trailer. Brand new wiring for entire trailer. Brand new submersible lights for tail lights. This trailer doesn't have brakes so only using a 4-wire. Brand new trailer plug attached to junction box and then 4 wire to rear. Each rear light is grounded to the frame(ring connector and metal was cleaned with grinder) and the common ground. The common ground is attached at the junction box to the wire going to the truck and also grounded to the trailer there. With the truck off and the headlight switch turned on, the trailer lights work. As soon as the ignition is turned on, the trailer lights flash on and off slowly. I have tried disconnecting the common ground with no change. If I disconnect 1 of the taillights, lights work as they should. It doesn't matter which taillight. Blinkers and brakes work as they should.
 
Not quite sure I actually figured it out, but found a solution. Just tested at this point and will install next week when I have a chance. Going to replace the submersible lights with a Nilight oval led with weld on bracket. Requiring a little more work, but I guess.

My thoughts are maybe the submersible don't pull enough for the truck to recognize.
 
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