I have a similar problem to a poster a few weeks ago.
My tach has all of a sudden started going nuts. It just goes bonkers.
The difference in mine and the guy from a few weeks ago is that I was at the end of a ride when this crazyness happens. the tach goes nuts and it starts missing and going crazy, BUT it will idle fine, however the tach still reads crazy.

If someone could decifer all this mess my bike is telling me I will be in your debt.

Thanks

Springer

If I remember right the advice was to check all connections especially earths.
I've not seen this myself (no tach). Check and clean all connections, including main battery connections. If in doubt take to the dealer.

Whiffi

I don't know if this will help anyone answer your question, but what year is your bike, the tach works diferently on '04 and later models.

Gary

I run dakota electronics, Come to find out it was a combination of a almost broke into POSITIVE battery connection. The end that connects to the bike, PAIN IN THE AS# to get back on. And a broke in half screw at the battery end, I guess I am lucky my crap ran as good as it did. I made a new battery lead from parts at the auto shop and bought a new battery while I was at it and the is back to her normal self again, all done in the carport without the large bill from a dealer thank goodness. :clap