Did you do anything electrical? Did anything get wet, when does the fuse blow? Does it blow on parking light position or on headlight position? Turn all your lights off, step on the brake, if all is good try your turn signals,what happens? If all is good turn on running lights. You need to start eliminating things.
Which fuse # ? Did you check fuse #1 behind glove box? Another thing to do is pull apart your tail lights and check for corrosion on the terminals or bulb socket, which would cause grounding issues to the tub.
May be a wire has cut through its insulation from vibrating against the body or frame and it's only doing it sporadically. I would start inspection at the lights and work back toward the switch and then fuse block. The wiring at the light sockets lives a pretty hard life on most cars, in my experience, with corrosion and vibration/rubbing can occur there, too.
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