If it was a 650 with cdi s and an old battery I would certainly think that the cdi were burned out by either somebody jump starting it with the family car or it just was unable to receive enough voltage at the cdi s overheating them and burning them out...that stuff happens all the time with those. But the newer 750 may not use the same cdi as the 650.
I have a 2001 750, and the thing I worry about ( don't know if the 96 has this) is that mystery black box that clips onto the molded battery cover that covers the battery just under the seat. Now , it isn't really the little black box itself that concerns me ,it's the wires that connect the box to the electrical system. When charging or changing one of these batteries , you have to unclip the black box from the cover and the wires are too short to put the black box out of the way safely, there's no level surfaces to lay it on, the length of the wires won't allow you to just flip it over onto the frame.... there's just no friggin place to put it while you F with the battery. That said it is the condition of the wires inside their plastic sleeves that concern me, sometimes wires can break inside the wire coating and from the outside it'll look good so who would suspect right ? But they can and do break on occasion like that and you wouldn't guess it's so until you multi meter both ends of each wire and find no ohms. I'm suspecting that you may have fallen victim to a wire breakage in this area from bending and falling movements over the years( if it is like the 2001 setup, it's bound to fail someday) perhaps this has happened on this machine?
