Also need to know are they many variants between main harness?
My bike had the alarm fitted, but does it have a different loom from the factory than the non alarm version?
No, I think you will find your bike has a standard Benelli loom and wiring harness. The problem lies with the "muppet" that fitted your alarm.
You would not believe the "hacks " I have found.
Best one yet is trying to find a power source , rather than go to the battery or fuse box, they went to the positive feed of the rear brake light switch.
they spliced into that and soldered in a cable feed wire 6 times the capacity of the brake light feed.
If they had looked they could have found a power 12v feed less than 150 mm from the cable .
Bike failed the MOT on no rear brake light. cos it was not being supplied with 12v power , due to the battery drain to other outlets.
Better still they had not heat shrunk the cable after soldering no ,can anyone remember the old fabric black insulation tape .
they sort of wrapped that round the joint. you had to see it to believe it .