I bought a Autometer Monster Tach about 1 year ago, and it has really not been used but for about 5000 miles. Now the tach needle jumps around by about 500+ RPM. It is hooked to an MSD 6AL. I do not think it needs an adapter, because otherwise why would it have worked fine for a while? I also tried rewiring the wire that runs from the box to the tach, and no luck. I also checked my ground...looked good. Any Ideas?

 

Idea: maybe its defective

 

that is weird.. if it worked great for a while and then all of a sudden its jumping that is kinda weird.
and if you checked all the connections for the tach maybe he is right an its going bad for some reason.

does that company have a 1800 toll free number i would call them up and tell them how you have the tach hooked up and what it is doing.