so what your saying is when you put it in reverse the fuse blows?
easy fix is to never go backwards
you need to go grab the light fuse replacement thingy off your neighbor again, plug it in and start looking, specially where the reverse light wiring runs through the door and stuff, see if there is a plug or connection where it connects back to the factory wiring and unplug it there and try it
I doubdt it will be in hte factory wiring but you never know