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First of all, I am not a wiring expert, but I have worked with car trailers before. Your problem could be caused by any number of things, including the ground. I have never worked with this particular problem before. On my trailer I had a side marker light short out and all of the trailer lights would not work properly. The way to solve this problem would be to buy an electrical tester - the kind with the light - to see where you have power and where you don't.
Are you talking about the bulb of the fuse blowing. If it is the fuse check to make sure there are not any cuts in the sheething around the wire, this could be causing a short.