I had issues with the wiring harness on my trailer also. I had gone thoroughly over the wires and checked every place where there is a crimp connection, and there are several. I do not like crimp connections, so I removed them all. I made each connection spliced and soldered and then used watertight heat shrink tubing. Never again an issue! In all fairness it takes a lot of time to do this and it is easier in production to just crimp. But. I did find a couple crimps that were poor and the wires just pulled out causing my lights blinking on and off down the road.
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