short in dash tach and tail lights

i asked this question before and everyone was right it was the fuse so i replaced the fuse and it was fine for a few days then the other day it blew again. now i just replaced it ,looked at it while i pulled the switch for my lights and watched blow as soon as ipulled it right before my eyes.. . . what is causing this fuse to blow . . i was using a 25 fuse. .