blows day time running light /back up light fuse.

Hello. I have a 1984 F150. The fuse for the daytime running lights and the back up lights don't work. If I replace the fuse they might work for the next 1 or 2 drives and it's blowen again. Can anyone tell me if there is any common problem, that causes this fuse to blow before I start tearing the wiring harness apart? Thanks for reading this.

Start @ the trailer light harness if it has one then check the harness going to the rear of the truck(tail light). almost always you will find a broken wire with corrosion in it back there.