My money's on an intermittent ground. You'll have to start under the "dash" and work your way back with your fancy new multimeter; set it on resistance and ground one probe then attach to the ground side of the tach connector and watch the meter while wiggling the leads.
A positive attitude may not solve all your problems, but it will annoy enough people to make it worth the effort. Herm Albright (1876 - 1944)
| 
