Shortcut could also be in the ignition lock.
Not so easy to borrow this from your friends bike, but worth a try.
Works only if there is no immobilizer in the locks!
An old trick is to connect a bulb instead of the fuse to the fuse-socket(T-connection).
The job for the bulb is to limit the electric power, so you can start your bike.
You are now able to check the cables (pressing, bending....), when your fingers find the fault, the bulb changes its brightness.
Darker means cable is ok now, brighter means shortcut.
Be carefull, bulb will get HOT