Stewky

Morning. Does anyone have any ideas as to why my Kawasaki gt550 1989 may have decided to stop working. The other day the bike started to run on 2 cylinders so I turned the bike off. When I tried to restart the bike absolutely nothing. Only think working was the neutral light. No brake lights horn indicators nothing at all? When I purchased the bike off eBay last week it came with a couple of old cdi units in a box. Could they be the cause? Any suggestions would be more than welcome. The battery is reading 12.5 volts across the terminals with my fluke. Thanks.