Sounds like you may have a wiring fault on the lighting circuits.Check for any chaffed or trapped cables.The wires to the rear lights can become unclipped under the seat and get squashed.You may also have a poor connection somewhere causing excessive current.
One other thing,when was the last time the fuel filter was changed?A bit of a long shot but I had a similar problem on a 851.It turned out to be a blocked filter overloading the electrics.
Just a thought.