If the fuses are not clearing, you don't have a "short".

What usually happens is the conductor breaks inside the insulation leaving an intermittent "Open ".

The tests are to lightly pull on a single wire in an area that has high flex. If the conductor is broken, the insulation will stretch. You could also run a temp jumper across the trunk wiring ( hopefully from from plug to plug . )

Super flex wire has very fine strands to cope with flexing, regular wire can be used and usually lasts long enough. In either case be sure to leave enough slack and avoid flexing in a small area.