1993 GMC Van Blowing fuses all the time

Fuel pump fuse blows when you shut down. Replace fuse it runs. Turn off. Blown fuse. This is with a new battery and starter. It's a recently purchased piece and was told it had an illusive "short" somewhere. We have isolated most of the "custom" lighting etc. Ran for a month before this. Battery was cooked, starter brushes were worn past the clips. Help !