strange tacho problem

[hazza2508]

got an unoriginal tacho on an xs1100RH - bought from america by the PO and i have no idea what it's off. it works fine when i rev the bike in neutral, but then is very shaky when im actually riding. gets to about 4-5k then just oscilates while the bike revs up to god knows what. the bikes running well in general. quite confused.

[bikerphil]

The tach gets it's signal from the alternator. The connector behind the fuse panel (3 white wires) can be corroded and not give the tach a clean signal. Clean 'em up and see if it improves. This cleaning will also improve the alternator's output voltage.