91 Caprice Rear Defroster Fuse Issuse

Ok. 91 chevy caprice 305 motor... For some reason the fuse for the rear defroster keeps blowing after I have it runnin or about 10 min or so. I replaced it like 4 times the other day. Even put a bigger one in then was suppose to be in. Please help. The fuse for the rear defroster has only that on it. Just one fuse solely for the rear defroster. thanks:screwy: :screwy:

You have a short somewhere, fix it before you burn the car down with your bigger fuses.