Moto Guzzi California Rev Counter?

My rev counter on my 2001Moto Guzzi California has started fluctuating up and down while i'm on the move. When sitting"idle"its steady, any ideas????

loose cable at gearbox end or gauge end

hello, i will be honest i am just throwing a thought/ idea out with this idea, as i really no very little about guzzi's however, do you know if the tacho/rev counter is electronic. if it is, it may be the alternator or rectifier is on the way out, this is just a idea, hopefully someone with more knowledge may know, may be a idea to do a voltage check on it whilst on idle and at revs.