Welcome to the forums! It could be the cigarette lighter socket that is at fault. The same thing happened to me a little while ago when I tried to use a cheap 12v air compressor from Repco. It would keep blowing my fuses, so I took the compressor back, swapped it for another one, and the new one didn't blow a fuse, but instead it blew the entire cigarette lighter socket

. Made a quick trip to the junkyard to get another socket and it was all fixed

(didn't use that crappy air compressor again though). Other than a blown socket, check for corrosion on the connections