As Ray said, what truck? Have you done any modifications to the truck? Was there ever any damage in its history?
If you’re talking about the factory 7 term trailer plug adapters commonly available at every truck stop, big box store, etrailer.com and what not, then there’s an issue with either your truck, trailer, or that specific adapter.
Does it blow when you have just the adapter in, or after you plug the trailer in?
It matters because if you can’t plug the adapter in without blowing the fuse, then the adapter is bad.
If it blows after you plug the trailer in, then the trailer is wired incorrectly.
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