I need a crash course on finding electrical shorts

98. Grand Cherokee 5.2, has been 24 mechanics now. None of them can find the short. Only way I can drive. It is by pulling the fuse for interior power along with the trailer power fuse (use a test light on the battery and seems like most of the Short is coming from the trailer, power area, but won’t go away completely until I pull the interior power as well.)

Need a book or something to help me understand the procedure for locating a Short. Helpful tools, etc..