I have a 91 FXSTC with a Harley Tach. On my ride today the tach started bouncing between 3000 and 5000 rpm while riding. If I stop the tach reads correctly. It's when the tach goes over 2000 rpm that the thing goes crazy. Thanks for any suggestions?

 

Mine, started doing the same thing,
when my voltage regulator went.

Now that I replaced it, all is fine again.

Dave